Geologic units containing andesite

Earth material > Volcanic rock > Intermediate volcanic rock

Andesite

A volcanic rock defined modally by Q/(Q+A+P) < 20% or F/(F+A+P) < 10%, P/(A+P) > 90%, and M < 35

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Arizona - California - Colorado - Idaho - Massachusetts - Maryland - Maine - Michigan - New Hampshire - New Mexico - Nevada - Oregon - Pennsylvania - South Dakota - Texas - Utah - Virginia - Washington - Wisconsin - Wyoming

Arizona

Cretaceous sedimentary rocks (Cretaceous): Tan sandstone (Dakota Sandstone) overlain by gray shale (Mancos Shale); deposited in beach, river delta, and shallow sea settings. The Mancos Shale is overlain by the Mesaverde Group (map unit Kmv). This unit includes related sandstone and shale exposed near Show Low, Morenci (Pinkard Formation), and around Deer Creek south of Globe. (about 88-97 Ma)
Cretaceous to Late Jurassic sedimentary rocks with minor volcanic rocks (Late Jurassic to Cretaceous): Sandstone and conglomerate, rarely forms prominent outcrops; massive conglomerate is typical near base of unit and locally in upper part. These deposits are nonmarine except in southeastern Arizona, where prominent gray marine limestone (Mural Limestone) forms the middle of the Bisbee Group. Sandstones are typically medium-bedded, drab brown, lithic-feldspathic arenites. Includes Bisbee Group (largely Early Cretaceous) and related rocks, Temporal, Bathtub, and Sand Wells formations, rocks of Gu Achi, McCoy Mountains Formation, and Upper Cretaceous Fort Crittenden Formation and equivalent rocks. (80-160 Ma)
Early Proterozoic metavolcanic rocks (Early Proterozoic): Weakly to strongly metamorphosed volcanic rocks. Protoliths include basalt, andesite, dacite, and rhyolite deposited as lava or tuff, related sedimentary rock, and shallow intrusive rock. These rocks, widely exposed in several belts in central Arizona, include metavolcanic rocks in the Yavapai and Tonto Basin supergroups. (1650 to 1800 Ma)
Early Tertiary to Late Cretaceous volcanic rocks (Late Cretaceous to Early Tertiary): Rhyolite to andesite and closely associated sedimentary and near-surface intrusive rocks; commonly dark gray to dark greenish gray or greenish brown. In the ranges west of Tucson, this unit includes thick welded ash-flow tuffs. Volcanic rocks of this unit are inferred to be derived from vents and volcanoes above magma chambers that solidified to form the granitic rocks of map unit TKg. These rocks are restricted to southeastern Arizona except for a small outcrop near Bagdad. (50-82 Ma)
Holocene to middle Pliocene basaltic rocks (Middle Pliocene to Holocene): Mostly dark-colored basaltic lava and cinders young enough that some original volcanic landforms are still apparent. Includes a small amount of andesite, dacite, and rhyolite. Rocks of this map unit are largely restricted to six areas widely distributed in Arizona: San Francisco and Uinkaret volcanic fields in northern Arizona (0-4 Ma); Springerville (0-4 Ma) and San Carlos (0-2 Ma) volcanic fields in east-central Arizona; and San Bernardino (0-1 Ma) and Sentinel (1-4 Ma) volcanic fields in southern Arizona. Rocks of this unit are also present in the extreme southwestern part of Arizona where they were erupted at the edge of the Pinacate volcanic field (0-2 Ma) in northwestern Sonora. (0-4 Ma)
Holocene to middle Pliocene volcanic rocks (Middle Pliocene to Holocene): Rhyolite to andesite deposited as a sequence of lava flows and associated rocks; generally light to medium gray, tan, or reddish brown. These rocks are part of the San Francisco volcanic field. (0-4 Ma)
Jurassic sedimentary and volcanic rocks (Jurassic): Sandstone and conglomerate derived from volcanic rocks with associated intermediate-composition lava flows, breccias, and tuffs. In southern Arizona this unit includes rocks of the Artesa sequence, Pitoikam Formation, Mulberry Wash volcanics, Rudolfo Red Beds, Recreation Red Beds, and Gardner Canyon Formation. In western Arizona it includes the Harquar Formation, rocks of Slumgullion, and related(?) unnamed units in the Kofa and Middle Mountains. This unit is characterized by maroon, brown, and purplish-gray volcanic-lithic sandstone and siltstone, with subordinate to abundant conglomerate, quartz-rich sandstone and sparse limestone. (150-170 Ma)
Late to middle Miocene basaltic rocks (Middle to Late Miocene): Mostly dark, mesa-forming basalt deposited as lava flows. Rocks of this unit are widely exposed south of Camp Verde (Hickey Formation basalts), in the Mohon Mountains north of Bagdad, "The Mesa" east of Parker, and at other scattered locations in western Arizona. Rocks of this unit were not tilted by middle-Tertiary normal faulting except in a narrow belt from north of Phoenix to the northwest corner of the state. (8-16 Ma)
Middle Miocene to Oligocene volcanic and sedimentary rocks, undivided (Oligocene to Middle Miocene): Sequences of diverse volcanic rocks with abundant interbedded sedimentary rocks. (11-32 Ma)
Middle Miocene to Oligocene volcanic rocks (Oligocene to Middle Miocene): Lava, tuff, fine-grained intrusive rock, and diverse pyroclastic rocks. These compositionally variable volcanic rocks include basalt, andesite, dacite, and rhyolite. Thick felsic volcanic sequences form prominent cliffs and range fronts in the Black (Mohave County), Superstition, Kofa, Eagletail, Galiuro, and Chiricahua Mountains. This unit includes regionally extensive ash-flow tuffs, such as the Peach Springs tuff of northwestern Arizona and the Apache Leap tuff east of Phoenix. Most volcanic rocks are 20-30 Ma in southeastern Arizona and 15 to 25 Ma in central and western Arizona, but this unit includes some late Eocene rocks near the New Mexico border in east-central Arizona. (11-38 Ma)
Pliocene to middle Miocene volcanic rocks (Middle Miocene to Pliocene): Rhyolite to andesite deposited as lava flows and related rocks associated with basaltic rocks of map units Tby and Tb. (2-12 Ma)

California

Cretaceous marine rocks (in part nonmarine), unit 2 (West Walker River) (Triassic(?) and/or Jurassic(?)): Undivided Cretaceous sandstone, shale, and conglomerate; minor nonmarine rocks in Peninsular Ranges
Jurassic marine rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Devonian to Late Jurassic): Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks
Paleozoic metavolcanic rocks, unit 2 (Northeastern Sierra Nevada) (Devonian and Permian): Undivided Paleozoic metavolcanic rocks. Mostly flows, breccia and tuff, including greenstone, diabase, and pillow lavas; minor interbedded sedimentary rocks
Paleozoic metavolcanic rocks, unit 6 (El Paso Mountains) (Devonian(?) and Permian): Undivided Paleozoic metavolcanic rocks. Mostly flows, breccia and tuff, including greenstone, diabase, and pillow lavas; minor interbedded sedimentary rocks
Permian marine sedimentary rocks, unit 3 (Northeastern Sierra Nevada) (Early to Late Permian): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks
Quaternary pyroclastic and volcanic mudflow deposits, unit 1 (Cascade Volcanic Field) (Quaternary): Quaternary pyroclastic and volcanic mudflow deposits.
Quaternary pyroclastic and volcanic mudflow deposits, unit 1, questionably identified (Cascade Volcanic Field) (Quaternary): Quaternary pyroclastic and volcanic mudflow deposits.
Quaternary pyroclastic and volcanic mudflow deposits, unit 3 (Sutter Buttes) (Quaternary (1.5-2.5 Ma)): Quaternary pyroclastic and volcanic mudflow deposits.
Quaternary volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 1, questionably identified (Cascade Volcanic Field) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 2 (Long Valley Caldera) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 3 (Clear Lake Volcanic Field) (Quaternary (0-4 Ma)): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 4 (Sutter Buttes) (Quaternary (1.5-2.5 Ma)): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 5 (Coso Volcanic Field) (Quaternary (0-4 Ma)): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 6 (Sierra Nevada) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 7 (Mojave Desert) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Quaternary volcanic flow rocks, unit 7, questionably identified (Mojave Desert) (Quaternary): Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.
Recent (Holocene) pyroclastic and volcanic mudflow deposits, unit 1 (Cascade Volcanic Field) (Holocene): Recent (Holocene) pyroclastic and volcanic mudflow deposits; in part Pleistocene.
Recent (Holocene) volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Holocene): Recent (Holocene) volcanic flow rocks; minor pyroclastic deposits; in part Pleistocene.
Recent (Holocene) volcanic flow units, unit 3 (Clear Lake Volcanic Field) (Holocene): Recent (Holocene) volcanic flow rocks; minor pyroclastic deposits; in part Pleistocene.
Tertiary intrusive rocks (hypabyssal), unit 1 (Cascades Volcanic Field) (Tertiary): Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.
Tertiary intrusive rocks (hypabyssal), unit 2 (Quien Sabe Volcanic Field) (Tertiary): Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.
Tertiary intrusive rocks (hypabyssal), unit 5 (Southern California Basin) (Tertiary): Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.
Tertiary intrusive rocks (hypabyssal), unit 6 (Southern Mojave Desert) (Tertiary): Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.
Tertiary pyroclastic and volcanic mudflow deposits, unit 1 (Sonoma Volcanic Field) (Tertiary (3-7 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary pyroclastic and volcanic mudflow deposits, unit 5 (Southern California Basin) (Tertiary (8-25 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary pyroclastic and volcanic mudflow deposits, unit 6 (Jacumba) (Tertiary (12-19 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary pyroclastic and volcanic mudflow deposits, unit 7 (Southern Mojave Desert) (Tertiary (8-28 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary pyroclastic and volcanic mudflow deposits, unit 8 (Northern Mojave Desert) (Tertiary (4-22 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary pyroclastic and volcanic mudflow deposits, unit 9 (Cascade Range) (Tertiary (2-24 Ma)): Tertiary pyroclastic and volcanic mudflow deposits.
Tertiary volcanic flow rocks, unit 10 (Alverson) (Tertiary (14-18 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 11 (Jacumba) (Tertiary (12-19 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 12 (Sam Emigdio) (Tertiary (22-25 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 13 (Plush Ranch-Vasquez-Diligencia) (Tertiary (19-23 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 15 (Southern Mojave Desert) (Tertiary (8-28 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 16 (Northern Mojave Desert) (Tertiary (4-22 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 17 (Cascade Range) (Tertiary (2-24 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 18 (San Joaquin-Kings Canyon) (Tertiary (3-4 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 1 (Quien Sabe-Burdell Mountain) (Tertiary (9.5-13 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 2 (Pinnacles-Neenach) (Tertiary (22-24 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 3 (Sonoma Volcanic Field) (Tertiary (3-7 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 5 (San Luis Reservoir) (Tertiary (7.5-9.5 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 6 (Page Mill-Mindego) (Tertiary (12-15 Ma)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Tertiary volcanic flow rocks, unit 8 (Southern California Basin) (Tertiary (8-25 Ma; most near 15)): Tertiary volcanic flow rocks; minor pyroclastic deposits.
Triassic marine rocks, unit 5 (Northern Sierra Nevada) (Middle to Late Triassic): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks

Colorado

Intra-ash flow andesitic lavas (Phanerozoic | Cenozoic | Tertiary)
Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Phanerozoic | Cenozoic | Tertiary): Includes several named units
South Park Fm (Phanerozoic | Cenozoic | Tertiary): Arkosic sandstone and shale, volcaniclastic conglomerate, and andesite flows and breccia

Idaho

Dacite to rhyolite (or rhodacite) ignimbrites; Eocene rhyodacitic cauldron complex; east-central Idaho, central Challis volcanic field (Eocene): Eocene mixed silicic and basaltic volcanic ejecta, flows and reworked debris.
Intrusive andesite, basalt, and diorite; Quaternary to Pliocene subvolcanic intrusions; southeastern Idaho (Quaternary to Pliocene)
Rhyolite, andesite, dacite, quartz latite; Oligocene to Eocene volcanics; northern Idaho; (Paleogene, possibly Oligocene): Lower Tertiary, possibly Oligocene, flows and tuffs of northern Idaho.
Rhyolite ignimbrites, basalt flows, andesitic flows and tuffs, mudstone, conglomerate, and limestone; Quaternary to Tertiary volcanics and sediments; east-central Idaho (Pliocene): Pliocene silicic welded tuff, ash, and flow rock; most common in southwestern Idaho.

Massachusetts

Newbury Volcanic Complex (Lower Devonian and Upper Silurian): Newbury Volcanic Complex - Porphyritic andesite, includes tuffaceous mudstone beds containing fossils of Late Silurian through Early Devonian age.
Newbury Volcanic Complex (Lower Devonian and Upper Silurian): Newbury Volcanic Complex - Lower members. Basalt, andesite, rhyolite, and tuff.

Maryland

Libertytown Metarhyolite (Late Precambrian (?)): Libertytown Metarhyolite - Purple, bluish-black, and red, dense, fine-grained metarhyolite with feldspar phenocrysts; interbedded with blue and purple amygdaloidal metaandesite; both rhyolite and andesite interbedded with blue, purple, and green phyllitic slates.

Maine

Devonian Edmunds Hill Andesite (Devonian): Devonian Edmunds Hill Andesite
Devonian - Silurian Thorofare Andesite (Devonian - Silurian): Devonian - Silurian Thorofare Andesite
Ordovician Lobster Mountain volcanic complex andesite member (Ordovician): Ordovician Lobster Mountain volcanic complex andesite member
Undifferentiated volcanic rocks of the Spider Lake and Chandler Pond Formations (Devonian - Silurian): Undifferentiated volcanic rocks of the Spider Lake and Chandler Pond Formations

Michigan

Copper Harbor Conglomerate; Volcanic member (Early Proterozoic): Copper Harbor Conglomerate; Volcanic member - Basaltic to andesitic volcanic flows interbedded within the conglomerate and sandstone
Dacite and volcanogenic graywacke (Early Proterozoic): Dacite and volcanogenic graywacke - Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.
Mafic metavolcanic rocks (Early Proterozoic): Mafic metavolcanic rocks - Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.
Menominee Group; Hemlock Formation (Early Proterozoic): Menominee Group; Hemlock Formation - Predominantly mafic to intermediate volcanic flows and pyroclastic rocks with interlayered slate and tuff beds
Porcupine Volcanics (Middle Proterozoic): Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
Portage Lake Volcanics (Middle Proterozoic): Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.
Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic): Powder Mill Group; Kallander Creek Volcanics - Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters
Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic): Powder Mill Group; Siemens Creek Volcanics - Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

New Hampshire

Ironbound Mountain Formation, Basaltic to andesitic member (Lower Devonian): Ironbound Mountain Formation, Basaltic to andesitic member.

New Mexico

andesite and basaltic andesite flows and associated volcaniclastic units (Phanerozoic | Cenozoic | Tertiary): Lower Tertiary, (Lower Oligocene and Eocene) andesite and basaltic andesite flows, and associated volcaniclastic units. Includes Rubio Peak Formation, and andesite of Dry Leggett Canyon
andesite flows (Phanerozoic | Mesozoic | Cretaceous): Uppermost Cretaceous andesite flows; restricted to southwestern area
andesites and basaltic andesites (Phanerozoic | Cenozoic | Tertiary): Upper Oligocene andesites and basaltic andesites (26-29 Ma); includes La Jara Peak Basaltic Andesite, Uvas Basalt, the basaltic andesite of Poverty Creek, and Squirrel Springs Andesite, the Razorback, Bear Springs Canyon, Salt Creek, Gila Flat, and Middle Mountain Formations, and the Alum Mountain Group; locally includes more silicic flows
andesitic volcanics (Phanerozoic | Mesozoic Cenozoic | Cretaceous Tertiary): Andesitic volcanics
basalt and andesite flows and vent deposits (Phanerozoic | Cenozoic | Quaternary): Basalt and andesite flows and locally vent deposits
basalt and andesite flows, Miocene (Phanerozoic | Cenozoic | Tertiary): Basalt and andesite flows; Miocene
basalt and andesite flows, Neogene (Phanerozoic | Cenozoic | Tertiary): Basalt and andesite flows; Neogene. Includes flows interbedded with Santa Fe and Gila Groups
basalt and andesite flows, Pliocene (Phanerozoic | Cenozoic | Tertiary): Basalt and andesite flows; Pliocene
basaltic and andesitic volcanics interbedded with sedimentary units (Phanerozoic | Cenozoic | Tertiary Quaternary): Basaltic and andesitic volcanics interbedded with Pleistocene and Pliocene sedimentary units
basaltic andesites (Phanerozoic | Cenozoic | Tertiary): Lower Miocene and uppermost Oligocene basaltic andesites (22-26 Ma). Includes Bearwallow Mountain Andesite and basaltic andesite of Mangas Mountain
rhyolitic pyroclastic rocks (Phanerozoic | Cenozoic | Tertiary): Upper Oligocene rhyolitic pyroclastic rocks (ash-flow tuffs); includes Davis Canyon Tuff, South Crosby Peak Formation, La Jencia, Vick's Peak, Lemitar, South Canyon, Bloodgood Canyon, Shelley Peak Tuffs, tuff of Horseshoe Canyon, Park Tuff, Rhyolite Canyon Tuff, Apache Springs Tuff, Diamond Creek, Jordan Canyon, Garcia Camp Tuffs, the Turkey Springs Tuff, the tuff of Little Mineral Creek, the Amalia Tuff, and others. Some contain volcaniclastic and reworked volcaniclastic rocks, and eolian sandstone; (24-29 Ma)
Santa Fe Group (Phanerozoic | Cenozoic | Tertiary Quaternary): Santa Fe Group, undivided. Basin fill of Rio Grande rift region; middle Pleistocene to uppermost Oligocene

Nevada

Andesite and basalt flows (Early Miocene to Early Pliocene): ANDESITE AND BASALT FLOWS-Mostly in about 17 to about 6 m.y. age range. In Humboldt County, locally includes rocks as old as 21 m.y. May include rocks younger than 6 m.y. in places
Andesite and related rocks of intermediate composition (Late Miocene to Middle Miocene): ANDESITE AND RELATED ROCKS OF INTERMEDIATE COMPOSITION-Flows and breccias
Andesite and related rocks of intermediate composition (Early Oligocene to Early Miocene): ANDESITE AND RELATED ROCKS OF INTERMEDIATE COMPOSITION-Flows and breccias
Andesite and related rocks of intermediate composition (Late Eocene to Middle Eocene): ANDESITE AND RELATED ROCKS OF INTERMEDIATE COMPOSITION-Flows and breccias
Basalt flows (Miocene to Quaternary): BASALT FLOWS-Locally includes maar deposits
Intrusive rocks of mafic and intermediate composition (Miocene to Quaternary): INTRUSIVE ROCKS OF MAFIC AND INTERMEDIATE COMPOSITION
Koipato Group and related rocks (Permian to Early Triassic): KOIPATO GROUP AND RELATED ROCKS (Lower Triassic)-Altered andesitic flows, rhyolitic tuffs and flows, and clastic rocks. Includes rocks mapped by Silberling (1959) as Pablo Formation and originally considered to be Permian in the Shoshone Mountains, Nye County. Includes Tallman Fanglomerate (Permian?) in Humboldt County
Limestone, minor amounts of dolomite, shale, and sandstone; locally thick conglomerate units (Triassic): LIMESTONE, MINOR AMOUNTS OF DOLOMITE, SHALE, AND SANDSTONE; LOCALLY THICK CONGLOMERATE UNITS (Lower, Middle, and Upper Triassic)-Includes Tobin, Dixie Valley, Favret, Augusta Mountain, and Cane Spring Formations and Star Peak Group in central Nevada and Grantsville and Luning Formations in west-central Nevada
Older basalt rocks (Early Oligocene to Early Miocene): OLDER BASALT ROCKS
Shale, chert, and minor amounts of quartzite, greenstone, and limestone (Ordovician): SHALE, CHERT, AND MINOR AMOUNTS OF QUARTZITE, GREENSTONE, AND LIMESTONE-Includes units such as Vinini Formation of north-central Nevada, Palmetto Formation in southern and central parts of Esmeralda County, and Comus Formation in Humboldt County. Locally includes rocks of Silurian and Devonian age.
Shale, sandstone, volcanogenic clastic rocks, andesite, rhyolite, and locally thick carbonate units (Late Triassic to Early Cretaceous): SHALE, SANDSTONE, VOLCANOGENIC CLASTIC ROCKS, ANDESITE, RHYOLITE, AND LOCALLY THICK CARBONATE UNITS-Undivided sequence locally containing recognizable equivalents of the Luning and Dunlap Formations
Volcanic flows and flow breccias, chiefly of andesitic composition, tuffs, sparse sandstone and graywacke (Permian to Jurassic): VOLCANIC FLOWS AND FLOW BRECCIAS, CHIEFLY OF ANDESITIC COMPOSITION, TUFFS, SPARSE SANDSTONE AND GRAYWACKE-Includes Happy Creek Volcanic Series and related rocks in Humboldt County and similar rocks in Washoe and Pershing Counties; includes andesite breccias and volcanogenic sedimentary rocks in Mineral County

Oregon

Andesite and dacite and sedimentary rocks (Miocene? and Oligocene) (Oligocene to Miocene): Lava flows, breccia, volcaniclastic and epiclastic rocks mostly of andesitic and dacitic composition; includes minor amounts of altered basaltic rocks. Joint surfaces and cavities commonly lined with hematite or montmorillonite clay, secondary silica minerals, zeolites, celadonite, or calcite. Andesite and dacite typically have plagioclase, hornblende, and clinopyroxene phenocrysts; some flows aphyric. Platy flow-jointing common. Age, mostly Oligocene; may include some rocks of early Miocene age. As shown, may include some rocks older than Oligocene, correlative with upper parts of unit Tea. One potassium-argon age of about 28 Ma on porphyritic hornblende andesite from Sheep Creek, southwest corner of Union County, indicates in part coeval with unit Tsf
Andesite (Holocene and Pleistocene) (Quaternary): Forms major stratovolcanoes dominantly of aphyric to porphyritic basaltic andesite and andesite; phenocrysts are principally pyroxene, olivine, plagioclase, and, rarely, hornblende. Locally includes dacite and minor basalt
Andesite (Pleistocene and Pliocene) (Pliocene to Pleistocene): Flows and flow breccia in the High Cascade Province composed dominantly of aphyric to porphyritic basaltic andesite and andesite. Mostly represents remnants of moderately to deeply eroded stratovolcanoes. Phenocrysts are mostly plagioclase, olivine, clinopyroxene, and lesser hypersthene and hornblende
Andesitic and basaltic rocks on Steens Mountain (Miocene): Called Steens Mountain Volcanic Series by Walker (1977); Steens Mountain Andesitic Series of Fuller (1931) and Williams and Compton (1953)
Basalt and andesite intrusions (Pliocene, Miocene, and Oligocene?) (Oligocene(?) to Pliocene): Sills, plugs and dikes of basaltic andesite, basalt, and andesite. Mostly represents feeders, exposed by erosion, for flows and flow breccias of units Tba and Trb. Includes a few dikes of hornblende and plagioclase porphyritic andesite, commonly altered, and aphyric basaltic andesite that probably were feeders for parts of unit Tub
Basalt and andesite (Miocene) (Miocene): Lava flows and breccia of aphyric and plagioclase porphyritic basalt and aphyric andesite; locally includes flow breccia, peperite, some palagonite tuff and breccia, and minor silicic ash-flow tuff and interbeds of tuffaceous sedimentary rocks. In Basin and Range and Owyhee Upland provinces unit grades upward into more silicic, andesitic, and quartz latitic flows and flow breccia, as well as some interbedded tuffs and ash-flow tuffs; also in this region includes aphyric and highly porphyritic, plagioclase-rich basalt. Interfingers with and grades laterally into units Tit and Tts. Commonly contains montmorillonite clays, zeolites, calcite, and secondary silica minerals as alteration products on fractures and in pore spaces. Age, mostly middle Miocene, but includes some rocks of early Miocene age based on vertebrate fossils from related sedimentary units and on potassium-argon ages that range from about 13 Ma to about 19 Ma; most isotopic ages are about 13 to 16 Ma. Includes Steens Basalt (Steens Mountain Basalt of Fuller, 1931) Owyhee Basalt of Corcoran and others (1962) and Kittleman and others (1967), Hunter Creek Basalt and "unnamed igneous complex" of Kittleman and others (1965, 1967), and flows of Prineville chemical type (Uppuluri, 1974; Swanson and others, 1979), which previously were considered part of the Columbia River Basalt Group (Swanson, 1969a)
Basalt and basaltic andesite (Pleistocene and Pliocene) (Pliocene to Pleistocene): Flows, flow breccia, and pyroclastic deposits. Flows are aphanitic to finely crystalline, commonly diktytaxitic, and aphyric to porphyritic. Textures are mostly intergranular grading to intersertal; some andesite flows are finely trachytic and a few basalt flows are subophitic. Phenocrysts, mostly unaltered, include bytownite and labradorite, olivine, calcic augite, and hypersthene. Flows and breccia form shields, lava cones, and valley fill; in places greatly dissected and modified by fluvial erosion. Includes Boring Lava of Trimble (1963) and Hampton (1972) and Battle Ax Basalts of Thayer (1936). Potassium-argon ages from this unit range from about 1.2 to 3.9 Ma; in places difficult to distinguish from youngest flows of unit Trb
Basaltic and andesitic rocks (upper and middle Miocene) (Middle to Late Miocene): Lava flows and flow breccia of hypersthene and olivine andesite, basaltic andesite containing plagioclase and pyroxene phenocrysts, and basalt; many flows contain phenocrysts of both hypersthene and augite. Includes interbedded volcaniclastic and epiclastic rocks mostly of andesitic composition, but partly of dacitic or rhyodacitic composition. Includes really restricted flows of silicic andesite or dacite. Upper part of unit mostly unaltered, although olivine crystals are locally altered to clay minerals. Lower parts commonly altered; secondary minerals include nontronite and saponite, chalcedony, calcite, and zeolites. Older parts of this unit locally are propylitically altered adjacent to larger intrusions. Erupted mostly from widespread, northwest- and north-trending dikes and dike swarms and related plugs and lava cones. Potassium-argon ages range from about 10 Ma to about 17 Ma. Much of this unit was previously assigned to the Sardine Formation (Peck and others, 1964), although the type locality of the Sardine Formation ("Sardine Series" as mapped by Thayer, 1939) may be older. Includes Elk Lake Formation (White, 1980a, 1980b), part of the Rhododendron Formation (Trimble, 1963; Wise, 1969), and andesite of Nohorn Creek of Hammond and others (1982)
Basaltic andesite and basalt (Holocene? and Pleistocene) (Quaternary): Flows and flow breccia dominantly of basaltic andesite containing plagioclase, olivine, and pyroxene phenocrysts and olivine-bearing basalt representing part of the volcanic sequence of the High Cascade Range (Thayer, 1937). Unit mostly forms small shield volcanoes, gentle-sided lava cones, and, in places, intracanyon flows
Basalt (upper and middle Miocene) (Middle to Late Miocene): Basalt flows, flow breccia, and basaltic peperite; minor andesite flows; some interbeds of tuff and tuffaceous sedimentary rocks. Basalt is aphyric to moderately porphyritic with phenocrysts of plagioclase and olivine and exhibits both subophitic and diktytaxitic textures. Includes Picture Rock Basalt of Hampton (1964), radiometrically dated by potassium-argon methods as middle(?) and late Miocene in age (see Fiebelkorn and others, 1983), flows of Deer Butte Formation of Kittleman and others (1967), and extensive unnamed flow sequences in the Basin-Range and Owyhee Upland Provinces of southern Lake, Harney, and Malheur Counties that are younger than Steens Basalt, dated at about 15 Ma (Baksi and others, 1967) and the Owyhee Basalt, dated at about 14 Ma (Bottomley and York, 1976; see also Fiebelkorn and others, 1983), and older than 7 or 8 Ma. Partly coeval with the Saddle Mountains Basalt of the Columbia River Basalt Group (Swanson and others, 1979)
Clastic rocks and andesite flows (lower Oligocene?, Eocene, and Paleocene?) (Paleocene to Early Oligocene): Mostly andesitic lava flows, domes, breccia, and small intrusive masses and lesser basaltic to rhyolitic rocks; interlayered saprolite, bedded volcaniclastic and epiclastic mudstone, claystone, siltstone, sandstone, conglomerate, and mudflow (lahar) deposits. Mostly consists of Clarno Formation of central Oregon and unnamed rocks of Basin and Range Province in south-central Oregon. Fossil plants and vertebrates in these rocks are Eocene in age. Andesite and basalt lava flows are typically slightly altered; most glass is devitrified and altered to clay minerals, zeolites, and secondary feldspar. Reliable K-Ar ages of rocks from unit range from about 54 Ma to about 37 Ma (Evernden and James, 1964; Fiebelkorn and others, 1983). A number of K-Ar ages on rocks shown on source maps as part of the Clarno Formation are in the range of about 36 to 19 Ma (Fiebelkorn and others, 1983). Although these rocks are lithologically similar to, but generally less altered than, rocks of the Clarno Formation, they are coeval with the John Day Formation. Most of these enigmatic rocks of Oligocene and early Miocene age are included in unit Tas. At base of unit in Blue Mountains Province, locally includes quartzose and feldspathic sandstone, siltstone, and shale largely of granitic or metamorphic provenance; fossil plants in these sedimentary rocks indicate an early Eocene or Paleocene age
Columbia River Basalt Group and related flows (Miocene) (Miocene): Subaerial basalt and minor andesite lava flows and flow breccia; submarine palagonitic tuff and pillow complexes of the Columbia River Basalt Group (Swanson and others, 1979); locally includes invasive basalt flows. Flows locally grade laterally into subaqueous pillow-palagonite complexes and bedded palagonitic tuff and breccia. In places includes tuffaceous sedimentary interbeds. Joints commonly coated with nontronite and other clayey alteration products. Occurs principally in the Willamette Valley from Salem north to the Columbia River, and in the northern Coast Range. Unit includes correlative Cape Foulweather and Depoe Bay Basalts in the Coast Range (Snavely and others, 1973, 1976a, 1976b; Swanson and others, 1979; Wells and others, 1983). In Eastern Oregon, occurs principally in Deschutes-Umatilla Plateau and in the Blue Mountains. K-Ar ages range from about 6 to about 16.5 Ma (McKee and others, 1977; Swanson and others, 1979; Sutter, 1978; Lux, 1982). Locally separated into Tcs, Tcw, Tcg, Tcp, and Tci
Flows and clastic rocks, undifferentiated (Miocene) (Miocene): Chiefly basaltic andesite and andesite lava flows and flow breccia containing plagioclase and pyroxene (hypersthene and augite) phenocrysts, mudflows (lahars), and volcanic conglomerates; locally includes some dacite flows. Includes lesser, coarse- to fine-grained epiclastic volcanic sedimentary rocks and ash-flow and air-fall tuffs. Partly equivalent in age to unit Tba and may be partly coeval with younger parts of unit Tstb. Locally altered adjacent to larger intrusions. The oldest radiometrically dated rocks assigned to this unit are about 17 Ma (Sutter, 1978); in part lapped by flows questionably assigned to unit Tba, radiometrically dated at about 10 Ma, and unconformably overlain by flows of unit Trb. Includes some of rocks formerly mapped as Sardine Formation and some mapped as Rhododendron Formation
Hypabyssal intrusive rocks (Miocene and Miocene?) (Miocene): Hypabyssal, medium-grained, hornblende diorite and quartz diorite in small stocks and large dikes; includes intrusions of medium- to fine-grained gabbro and plugs and small stocks of medium-grained, holocrystalline, olivine andesite. Also includes medium-grained, commonly porphyritic biotite quartz monzonite and leucocratic granodiorite. Many of these intrusive bodies are moderately to intensely propylitized, as are wallrocks they intrude; locally, along shears, the rocks also are sericitized. Potassium-argon ages on several of these shallow intrusions range from about 8 Ma to about 22 Ma (Wise, 1969; Bikerman, 1970; Sutter, 1978; Power and others, 1981a, b; Fiebelkorn and others, 1983)
Intrusive basalt and andesite (Pleistocene, Pliocene, and Miocene) (Miocene to Pleistocene): Sills, plugs and dikes of basaltic andesite, basalt, and andesite. In the Cascade Range most of these represent feeders, exposed by erosion, for flows and flow breccias of units Tba and Trb and a few are feeders for units QTba and QTa; in foothills of western Cascades includes several sins and dikes that may represent feeders for flows in unit Tu. May include some invasive flows. Includes a few dikes of hornblende and plagioclase porphyritic andesite, commonly altered, that probably were feeders for parts of unit Tu
Mafic and intermediate intrusive rocks (Pliocene and Miocene) (Miocene to Pliocene): Dikes, plugs, and sills of basalt, diabase, gabbro, and lesser andesite that fed many of the Miocene basalt and andesite flows in units Tc and Tba. Some intrusions are rootless and are invasive into sedimentary sequences; includes related breccia and peperite. Includes the Monument dike swarm of northwestern Grant County (OR061), the Chief Joseph dike swarm principally in Baker and Wallowa Counties (OR093), the Steens Mountain dike swarm in Harney County (OR005; OR094; OR095) and numerous isolated intrusive bodies in southern Lake County and several intrusive masses in and near-vent flows in southern Malheur County (OR023;OR024). May also include some lower Pleistocene(?) rocks
Mafic and intermediate vent rocks (Pliocene? and Miocene) (Miocene to Pliocene): Basaltic and andesitic agglomerate, breccia, scoria, cinders, flows, and intrusive masses forming lava cones and small shields
Mafic and intermediate vent rocks (Pliocene? and Miocene) (Miocene to Pliocene): Basaltic and andesitic agglomerate, breccia, scoria, cinders, flows, and intrusive masses forming lava cones and small shields
Mafic vent and intrusive rocks (Eocene?) (Eocene): Mostly plugs, dikes, and irregular intrusive bodies of basaltic andesite and porphyritic hornblende or pyroxene andesite. Represents some of vents for unit Tca and possibly for unit Tas
Mafic vent complexes (Miocene) (Miocene): Intrusive plugs and dike swarms and related near-vent flows, breccias, cinders, and agglutinate of basaltic andesite, basalt, and andesite; commonly in the form of eroded piles of red, iron-stained thin flows, cinders, and agglutinate cut by mafic intrusions
Mafic vent complexes (Pleistocene, Pliocene, and Miocene?) (Late Miocene to Pleistocene): Plugs, dikes, and related near-vent flows, breccia, cinders, and agglutinate of basalt, basaltic andesite, and andesite; commonly in the form of either little-modified lava cones or partly eroded piles of reddish, iron-stained thin flows and fragmental ejecta cut by mafic intrusions. May also include rocks of late Miocene(?) age
Mafic vent deposits (Pleistocene, Pliocene, and Miocene?) (Miocene to Pleistocene): Mostly in small stratovolcanoes or shield volcanoes and lava cones of basalt and andesite. Includes agglomerate, breccia, scoria, cinders, ash, restricted flows, and small basaltic intrusive bodies. Transitional into pyroclastic rocks of cinder cones (QTp). May also include rocks of late Miocene(?) age
Marine facies (Middle Eocene to Late Eocene): Basaltic clastic rocks and pillow lavas, locally mapped separately by Wells and others (1983). Foraminiferal assemblages are assigned to the lower part of the Narizian Stage of Mallory (1959); see Wells and others (1983) for summary
Marine facies (Middle Eocene to Late Eocene): Basaltic clastic rocks and pillow lavas, locally mapped separately by Wells and others (1983). Foraminiferal assemblages are assigned to the lower part of the Narizian Stage of Mallory (1959); see Wells and others (1983) for summary
Mazama ash-flow deposits (Holocene) (Holocene): Rhyodacitic to andesitic ash-flow deposits related to climactic eruptions of Mount Mazama about 6,845 yr B.P. (14C) (Bacon, 1983)
Mazama pumice deposits (Holocene) (Holocene): Primary and reworked air-fall rhyodacite pumice related to climactic eruptions of Mount Mazama about 6,845 yr B.P.(14C). Mapped only where it extensively covers older units
Olivine basalt (Pliocene and Miocene) (Miocene to Pliocene): Thin, commonly open-textured (diktytaxitic), subophitic to intergranular olivine basalt flows, intercalated with and grades laterally through palagonite breccia and tuff into tuffaceous sedimentary rocks (unit Ts). In places includes flows of platy olivine andesite or basaltic andesite. Several potassium-argon ages ranging from about 4 to 7 Ma indicate unit is mostly of early Pliocene and late Miocene age. Includes Shumuray Ranch Basalt and Antelope Flat Basalt of Kittleman and others (1965), Grassy Mountain Basalt of Corcoran and others (1962), Drinkwater Basalt of Bowen and others (1963), basalt formerly assigned to Danforth Formation by Piper and others (1939) (see Walker, 1979), Hayes Butte Basalt of Hampton (1964), Pliocene and upper Miocene basalt flows capping and interstratified with the Madras (or Deschutes) Formation, and basalt flows interstratified in the Dalles Formation of Newcomb (1966; 1969)
Olivine basalt (Pliocene and Miocene) (Miocene to Pliocene): Thin, commonly open-textured (diktytaxitic), subophitic to intergranular olivine basalt flows, intercalated with and grades laterally through palagonite breccia and tuff into tuffaceous sedimentary rocks (unit Ts). In places includes flows of platy olivine andesite or basaltic andesite. Several potassium-argon ages ranging from about 4 to 7 Ma indicate unit is mostly of early Pliocene and late Miocene age. Includes Shumuray Ranch Basalt and Antelope Flat Basalt of Kittleman and others (1965), Grassy Mountain Basalt of Corcoran and others (1962), Drinkwater Basalt of Bowen and others (1963), basalt formerly assigned to Danforth Formation by Piper and others (1939) (see Walker, 1979), Hayes Butte Basalt of Hampton (1964), Pliocene and upper Miocene basalt flows capping and interstratified with the Madras (or Deschutes) Formation, and basalt flows interstratified in the Dalles Formation of Newcomb (1966; 1969)
Porphyritic basalt (upper Eocene) (Late Eocene): Subaerial lava flows and breccia of porphyritic basalt, minor basaltic andesite, and rare dacite. Includes basalt of Cascade Head (Wells and others, 1983), Yachats Basalt (Snavely and others, 1976c) and Goble Volcanic Series (Warren and others, 1945). Also includes camptonitic extrusive rocks (tuff breccia, lapilli tuff, and minor pillow flows) interbedded in Nestucca Formation
Pyroclastic ejecta of basaltic and andesitic cinder cones (Holocene, Pleistocene, Pliocene, and Miocene?) (Miocene to Holocene): Mostly unconsolidated, oxidized, fine to coarse, scoriaceous cinders, bombs, and agglutinate deposited in subaerial environment
Pyroclastic ejecta of basaltic cinder cones (lower Pliocene? and Miocene?) (Miocene to Early Pliocene): Mostly unconsolidated, oxidized, fine to course, scoriaceous cinders, bombs, and agglutinate deposited in subaerial environment
Rhyolite and dacite (Pliocene? and Miocene) (Miocene to Pliocene): Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 +/- 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna
Rhyolite and dacite (Pliocene? and Miocene) (Miocene to Pliocene): Ash-flow tuff, lava flows, pumice-lapilli tuff, coarse pumicite, flow breccia, and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; in places includes peralkaline rhyolite and some andesite and andesite breccia. Locally porphyritic with phenocrysts of alkali feldspar, plagioclase, and minor augite, ferro-hedenbergite, hornblende, hypersthene, or biotite. Commonly flow banded; locally glassy. Many of the ash--flow tuffs exhibit flow features and only obscure vitro-clastic textures. In places includes interlayers of silicic volcaniclastic rocks and tuffaceous sedimentary rocks. Includes rhyolite at Owyhee Dam, Jump Creek Rhyolite, and Littlefield Rhyolite, all of Kittleman and others (1965); Dooley Rhyolite Breccia of Gilluly (1937), radiometrically dated at 14.7 +/- 0.4 Ma by potassium-argon methods (Fiebelkorn and others, 1983); resurgent domal masses in McDermitt caldera area; and extensive unnamed flows and ash-flow tuffs in the central and southern part of the Owyhee Upland. Also includes isolated masses of dacitic and rhyodacitic flows, breccia, and ash-flow tuff along eastern slope of Cascade Range that are lapped by flows and sediments of the Madras (or Deschutes) Formation. Potassium-argon ages on rocks in unit from southeast Oregon range from about 13 to 16 Ma; lenses of interbedded tuffaceous sedimentary rocks locally contain a Miocene (Barstovian) vertebrate fauna
Rhyolitic tuff, tuffaceous sedimentary rocks, and lava flows (lower Miocene, Oligocene, and uppermost Eocene?) (Late Eocene to Early Miocene): Rhyolitic to dacitic varicolored bedded tuff, lapilli tuff, and fine- to medium-grained tuffaceous sedimentary rocks with interstratified welded and nonwelded ash-flow tuff and interbedded basalt and andesite flows. Also includes minor rhyolite and dacite flows and domes. Glass in tuff and tuffaceous sedimentary rocks is commonly altered to zeolites, clay minerals, and small amounts of opal, chalcedony, orthoclase, and calcite. Fossil plants and vertebrates indicate an Oligocene and Miocene age. Locally a late Hemingfordian age indicated by mammalian fauna (Woodburn and Robinson, 1977). May include some rocks of middle Miocene age in the area west and northwest of Lakeview. Potassium-argon ages on rocks from unit range from about 36 Ma (Swanson and Robinson, 1968) to about 20 Ma. Includes Pike Creek Formation of Walker and Repenning (1965), originally identified as Pike Creek Volcanic Series by Fuller (1931), and unnamed volcanic and volcaniclastic rocks of southern Lake County, some of which have been correlated with the Miocene and Oligocene Cedarville Formation of northeastern California
Sedimentary and volcanic rocks, partly metamorphosed (Paleozoic) (Paleozoic): Undifferentiated sedimentary and volcanic rocks some of which are highly deformed and locally metamorphosed to amphibolite and schist. Occurs mostly in Strawberry and Aldrich Mountains of the Blue Mountains province. Includes undivided Paleozoic rocks and Paleozoic volcanic rocks of Brown and Thayer (1966) and Dixie Butte Meta-andesite of Brooks and others (1984)
Sedimentary rocks (Jurassic) (Late Jurassic ): Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In Klamath Mountains of southwest Oregon, includes Galice Formation (Wells and Peck, 1961) and unnamed, hornblende- and (or) pyroxene-bearing clastic rocks of Jurassic age (Smith and others, 1982)
Strawberry Volcanics (Pliocene? and Miocene) (Miocene to Pliocene): Flows and flow breccia of basalt, basaltic andesite, and andesite; includes restricted domal complexes and related flows and breccia of rhyolite and dacite (Thayer, 1957; Brown and Thayer, 1966). Potassium-argon ages are mostly in the range of 12 to 20 Ma (Robyn, 1977; Fiebelkorn and others, 1983)
Subaqueous pyroclastic ejecta of basaltic and andesitic cinder cones (Holocene, Pleistocene, Pliocene, and Miocene?) (Miocene to Holocene): Partly consolidated, palagonitized, fine to coarse, scoriaceous altered cinders, bombs, breccia, and minor agglutinate, mostly deposited in subaqueous environment. Commonly with some interlayers and intermixed lacustrine sedimentary rocks. Forms palagonitic tuff and breccia cones and rings (maars) and, in places, palagonitic tuff ridges
Thin flows of basalt and andesite (Late Eocene to Early Miocene): Part of unit Tsfj; exact age uncertain
Tillamook Volcanics (upper and middle Eocene) (Middle Eocene to Late Eocene): Subaerial basaltic flows and breccia and submarine basaltic breccia, pillow lavas, lapilli and augite-rich tuff with interbeds of basaltic sandstone, siltstone, and conglomerate. Includes some basaltic andesite and, near the top of the sequence, some dacite. Potassium-argon ages on middle and lower parts of sequence range from about 43 to 46 Ma (Magill and others, 1981): one potassium-argon age from dacite near top of sequence is about 40 Ma (see Wells and others, 1983)
Tuffaceous sedimentary rocks and tuffs (lower? Pleistocene or Pliocene) (Pliocene to Early Pleistocene): Rhyolitic to andesitic ash-flow tuffs, pumice-fall deposits, minor mud flows, and older alluvium on the flanks of Newberry volcano (MacLeod and others, 1981; 1982) and in areas west and northwest of Bend
Undifferentiated tuffaceous sedimentary rocks, tuffs, and basalt (Miocene and Oligocene) (Oligocene to Miocene): Heterogeneous assemblage of continental, largely volcanogenic deposits of basalt and basaltic andesite, including flows and breccia, complexly interstratified with epiclastic and volcaniclastic deposits of basaltic to rhyodacitic composition. Includes extensive rhyodacitic to andesitic ash-flow and air-fall tuffs, abundant lapilli tuff and tuff breccia, andesitic to dacitic mudflow (lahar) deposits, poorly bedded to well-bedded, fine- to coarse-grained tuffaceous sedimentary rocks, and volcanic conglomerate. Originally included in Little Butte Volcanic Series (Peck and others, 1964); includes Mehama Volcanics and Breitenbush Tuffs or Series of Thayer (1933, 1936, 1939), Breitenbush Formation of Hammond and others (1982), Mehama Formation of Eubanks (1960), and Molalla Formation of Miller and Orr (1984a). In Columbia River Gorge, includes Miocene and older rocks previously assigned to the Skamania Volcanic Series (Trimble, 1963), or to the Eagle Creek Formation (Waters, 1973). Lower parts of unit exhibit low-grade metamorphism with primary constituents altered to clay minerals, calcite, zeolites (stilbite, laumontite, heulandite), and secondary silica minerals. In contact aureoles adjacent to stocks and larger dikes of granitic and dioritic composition or in areas of andesitic dike swarms, both wallrocks and intrusions are pervasively propylitized; locally rocks also have been subjected to potassic alteration. Epiclastic part of assemblage locally contains fossil plants assigned to the Angoonian Stage (Wolfe, 1981) or of Oligocene age. A regionally extensive biotite-quartz rhyodacite ash-flow tuff, the ash-flow tuff of Bond Creek of Smith and others (1982), is exposed in southern part of Western Cascade Range near and at base of unit. A K-Ar age of 34.9 Ma was determined on biotite from the tuff (Smith, 1980). Ash-flow tuffs, higher in the section and in the same area, have been radiometrically dated at 22 to 32 Ma by potassium-argon methods (J.G. Smith, unpublished data; Evernden and James, 1964; Fiebelkorn and others, 1983). In the central part of the Western Cascade Range, the unit has yielded a number of K-Ar ages in the range of about 32 to 19 Ma (Verplanck, 1985, p. 53-54). A fission-track age of 23.8 +/- 1.4 Ma was obtained on a red, crystal-rich ash-flow tuff (J.A. Vance, oral communication, 1983) collected at an elevation of about 3,000 ft on U.S. Highway 20 west-southwest of Echo Mountain. Most ages from basalt and basaltic andesite lava flows are in the range of about 35 to 18 Ma. Locally intruded by small stocks of granitoid rocks and by dikes, sills, plugs, and invasive flows of basaltic andesite and basalt; in many places, the intrusions are indistinguishable from poorly exposed interbedded lava flows; K-Ar ages on several of the mafic intrusions or invasive flows are about 27 to 31 Ma. In places subdivided into Tus, Tut, and Tub
Volcanic and metavolcanic rocks (Upper Triassic) (Late Triassic): Green to gray spilite and keratophyre flows and flow breccia; and subordinate amounts of coarse volcaniclastic sandstone, tuff, sandstone, siltstone, chert, conglomerate, and limestone. Marine fauna from interlayered sedimentary rocks indicates unit is mostly of Karnian (Late Triassic) age. Includes Late Triassic "andesitic and basaltic rocks" of Nolf and Taubeneck (1963), and the basaltic to rhyolitic metavolcanic rocks and interbedded sedimentary rocks of the Huntington Formation of Brooks (1979). Equivalent, in part, to unit TrPv
Volcanic rocks (Jurassic) (Late Jurassic): Lava flows, flow breccia, and agglomerate dominantly of plagioclase, pyroxene, and hornblende porphyritic and aphyric andesite. Includes flow rocks that range in composition from basalt to rhyolite as well as some interlayered tuff and tuffaceous sedimentary rocks. Commonly metamorphosed to greenschist facies; locally foliated, schistose or gneissic. Includes the Rogue Formation and volcanic rocks commonly assigned to the Galice Formation (Wells and Walker, 1953; Wells and Peck, 1961). Considered to be accreted island-arc terrane
Volcanic rocks (Triassic and Permian) (Triassic and (or) Jurassic): Massive flows of porphyritic meta-andesite, metabasalt, spilite, and keratophyre, volcanic breccia, and subordinate amounts of fine-grained volcaniclastic rocks. In southwest Oregon includes hornblende, pyroxene, and plagioclase porphyritic andesite flows, breccia, agglomerate, tuff, and locally, some basalt flows and dacitic tuffs of the Applegate Group
Youngest basalt and basaltic andesite (Holocene) (Holocene): Little-modified flows and associated breccia of basaltic andesite and some basalt in both central part of Cascade Range and on slopes of Newberry Volcano. Relations to Mazama pumice deposits indicate most of these rocks are less than 6,800 yr old (14C); isotopic ages on flows range from about 1,000 to 6,000 yr B.P. (14C)

Pennsylvania

Jonestown Volcanic Suite (Ordovician): Jonestown Volcanic Suite - Andesite extrusives and dark-greenish-gray metadiabase. Metadiabase weathers medium gray to brown, forming rounded cobbles and boulders.

South Dakota

Latitic Intrusive Rocks (Phanerozoic | Cenozoic | Tertiary | Paleocene Eocene): Dark-gray to greenish-gray laccoliths and sills of latite, latitic andesite, and quartz latite. Contains phenocrysts of andesine, oligoclase, biotite, hornblend, and sphene in a finely crystalline andesine-biotite-quartz groundmass.

Texas

Chinati Mountains caldera volcanic rocks, including Chinati Mountains Group, Mitchell Mesa Ignimbrite, and type area of Petan Basalt (Phanerozoic | Cenozoic | Tertiary | Oligocene): Chinati Mountains caldera volcanic rocks, including Chinati Mountains Group, Mitchell Mesa Ignimbrite, and type area of Petan Basalt
Chisos Formation of Schiebout et al (1987) and the Big Yellow Sandstone Member of their Tornillo Formation, undivided (Phanerozoic | Cenozoic | Tertiary | Eocene Oligocene): Chisos Formation of Schiebout et al (1987) and the Big Yellow Sandstone Member of their Tornillo Formation, undivided
Delaho and Rawls Formations, undivided (Phanerozoic | Cenozoic | Tertiary | Oligocene Miocene): Delaho and Rawls Formations, undivided NOTE: This unit is represented within the map unit explanation of (Geol. Map of Texas, 1992, Bur. Econ. Geol.) but does not occur on the map and is NOT included in the spatial data.
Eocene intrusive rocks (Phanerozoic | Cenozoic | Tertiary | Eocene): Eocene intrusive rocks
Infiernito caldera volcanic rocks including Capote Mountain Tuff, Tsh2 of Shely Group, Buckshot Ignimbrite, and Tm1 of Morita Ranch Formation (Phanerozoic | Cenozoic | Tertiary | Eocene-Late): Infiernito caldera volcanic rocks including Capote Mountain Tuff, Tsh2 of Shely Group, Buckshot Ignimbrite, and Tm1 of Morita Ranch Formation
Oligocene intrusive rocks (Phanerozoic | Cenozoic | Tertiary | Oligocene): Oligocene intrusive rocks
Van Horn Mountains caldera volcanic rocks (Phanerozoic | Cenozoic | Tertiary | Eocene): Van Horn Mountains caldera volcanic rocks

Utah

Miocene andesites (Tertiary)
Oligocene volcanic rocks (Late Eocene to Oligocene)

Virginia

Valley and Ridge Igneous Intrusions; Basalt (Jurassic-Tertiary): Valley and Ridge Igneous Intrusions; b: Basalt - Dikes in Augusta and Rockingham Counties: nepheline syenite, teschenite-syenite, and teschenite-picrite. Igneous bodies in Highland County: andesite and basalt.

Washington

Carboniferous and Permian volcanic rocks (Devonian to Permian; Triassic in Asotin County): Predominantly altered andesite, basalt, and diabase with interbedded chert and argillite; includes some tuff, greenstone, and spilitic volcanic rocks; northern Cascade Mountains. Mostly schistose greenstone, some agglomerate, and rarely lapilli; includes minor beds of limestone with associated argillite and graywacke; northwestern Stevens County.
Carboniferous-Permian sedimentary and volcanic rocks (Devonian to Permian; some Jurassic): Sedimentary and volcanic rocks, undivided. Cherty and slaty argillite, siltstone, graywacke, chert, greenstone, tuff, andesite, and spilitic volcanics.
Devonian rocks (Devonian to Permian): Thin alternating beds of cherty quartzite and argillite, occasional limestone lenses, volcanic rocks, sandstone, and graywacke on northwest shore of Orcas Island. Small outcrops of Devonian limestone included under Pzu in southeastern Stevens County and under PMPms in northwestern Whatcom County.
Eocene nonmarine rocks (Eocene): Predominantly sandstone and shale. Includes some conglomerate in the Cle Elum area in Kittilas County. Contains extensive coal seams near Roslyn and carbonaceous shale and coal beds in White Pass area. Contains tuff beds in northwestern Ferry County.
Eocene-Oligocene volcanic rocks (Eocene-Oligocene): Predominantly light-green, bedded andesite breccia with interbedded andesite and basalt flows, mudflows, and tuff beds; becomes more tuffaceous near top of unit. Includes tuffaceous and arkosic sandstone, shale, and carbonaceous shale beds in central and southern Cascade Mountians. Rhyodacite and quartz latite flows in northwestern Ferry County.
Eocene volcanic rocks (Eocene ): Predominantly andesite flows and breccia; includes interbedded sedimentary rocks south of Startup in Snohomish and King Counties.
Lower Tertiary volcanic rocks, undivided (Eocene): Predominantly andesite flows and flow breccia; includes basalt flows, minor rhyolitic rocks, and some sedimentary rocks.
Mesozoic volcanic rocks, undivided (Jurassic): Includes latite, andesite and basalt flows, tuff, and agglomerate. Interbedded sedimentary rocks in Orient area of Stevens County.
Middle Jurassic volcanic rocks (Middle Jurassic): Andesite, dacite, and minor basalt with slate and graywacke interbeds in the Nooksack River region of Whatcom County.
Miocene-Pliocene volcanic rocks (Miocene-Pliocene): Dark-gray, fine-grained, dense, porphyritic in part, basalt flows in central and south-central part of State; commonly interbedded with conglomerate, sandstone, and siltstone. Includes small areas of rhyolite north of Cle Elum in Kittitas County, and andesite north of Leavenworth in Chelan County.
Miocene volcanic rocks (Middle Miocene): Dark-gray to black, dense aphanitic basalt flows; commonly columnar jointed, less commonly irregularly and platy jointed; some flows vesicular, grading to scoriaceous; includes minor pillow lava, palagonite beds, and interbedded soil profiles and sedimentary beds; contains diatomite beds locally. Maximum thickness in south-central Washington may be in excess of 10,000 feet; much thinner in western Washington, where flows are mostly associated with marine sedimentary rocks. Includes acidic and intermediate volcanic rocks in northern Cascade Mountains.
Oligocene-Miocene volcanic rocks (Miocene): Andesite flow breccia, andesite flows, and minor tuff beds; includes some basalt flows and flow breccia. Commonly more massive and less altered than similar-appearing Eocene-Oligocene volcanic rocks. Clastic flows and flows of black glass, and course to fine-grained clastic and pyroclastic rocks in the Republic and Curlew areas of Ferry County.
Oligocene nonmarine rocks (Oligocene): Andesite conglomerate, tuff beds, and mudflow material. Includes some interbedded andesite flows in Columbia River Gorge. Lake sediments with Oligocene flora in Republic area in Ferry County. Massive tuffaceous sandstone and siltstone with beds of coal and high-alumina clay in Castle Rock-Toledo coal district in Cowlitz and Lewis Counties; include local interbedded basalt flows and some marine and late Eocene rocks.
Oligocene volcanic rocks (Oligocene): Andesite and rhyodacite flows, tuff, and tuffaceous sandstones of northern Lincoln County and southwestern Stevens County.
Pliocene-Pleistocene volcanic rocks (Mostly Pleistocene): Light-gray andesite, andesite porphyry, and open-textured basalt flows with minor associated mudflows and breccia. Includes restricted areas of valley flow basalt in Snake River Canyon in southeastern Washington and in Spokane area.
Pre-Carboniferous intrusive rocks (Paleozoic): Meta-quartz diorite, hypersthene diorite, and gneissose and directionless quartz diorite of eastern Skagit County. Quartz diorite and diorite in the San Juan Islands. Includes amphibolite and gneiss locally.
Tertiary dikes, sills, and small intrusive bodies (Middle to Late Tertiary): Dikes are commonly diabase; plugs and sills are generally andesite porphyry and dacite.
Tertiary granitic rocks (Probably mostly Eocene; ranges from Miocene to Paleocene): Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes dacite porphyry and granite breccia near Bumping Lake, Yakima County.
Tertiary volcanic rocks, undivided (Mostly Oligocene-Eocene): Includes andesite, basalt, and rhyolite flows, and associated pyroclastic rocks. In isolated areas across the northern part of the State.
Upper Eocene volcanic rocks (Late Eocene): Predominantly andesite flows and breccia; includes some basalt flows. Contains basaltic conglomerate, pyroclastic rocks, tuff beds, and sandstone in Chehalis-Centralia coal district, Lewis County.
Upper Eocene volcanic rocks (Late Eocene): Andesite and basalt flows and associated breccia in central Lewis County. Pyroclastic rocks, mudflows, flow breccia, and volcanic-rich sedimentary rocks in King and Pierce Counties.
Upper Eocene volcanic rocks (Late Eocene to Oligocene): Predominantly basalt flows and flow breccia; includes some pyroclastic and andesite rocks. Chiefly in western Washington.
Upper Eocene volcanic rocks (Late-Middle Eocene): Rhyolite flows and some interbedded tuff beds in Cle Elum area, Kittitas County.
Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Cretaceous-Jurassic): Sedimentary and volcanic rocks, undivided. Graywacke, argillite, siltstone, slate, volcanic rocks, phyllite, greenschist, and greenstone.
Upper Tertiary volcanic rocks, undivided (Miocene-Oligocene): Mostly massive andesite flows, flow breccia, and pyroclastic material; includes some basalt flows and sedimentary rocks.

Wisconsin

Bimodal mafic and felsic metavolcanic rocks (Early Proterozoic): Bimodal mafic and felsic metavolcanic rocks - High-aluminum basalt to low-silica andesite pillowed flows and interlayered dacite to rhyolite tuffs and porphyries in Monico and Mountain areas, northeastern Wisconsin. A rhyolite porphyry at Jennings (Oneida County) has an age of 1869 +/- 6 Ma. Rocks are host to massive sulfide deposits (Crandon and Pelican River)
Dacite and volcanogenic graywacke (Early Proterozoic): Dacite and volcanogenic graywacke - Includes andesite tuff. Occurs in northeastern Wisconsin. Dacite has age of 1866 +/- 39 Ma.
Mafic metavolcanic rocks (Early Proterozoic): Mafic metavolcanic rocks - Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.
Porcupine Volcanics (Middle Proterozoic): Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
Portage Lake Volcanics (Middle Proterozoic): Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.
Powder Mill Group; Kallander Creek Volcanics (Middle Proterozoic): Powder Mill Group; Kallander Creek Volcanics- Basalt, andesite and lesser rhyolite flows. Basalt flows near base of the formation contain plagioclase phenocrysts, some in radiating clusters
Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic): Powder Mill Group; Siemens Creek Volcanics- Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Wyoming

Absaroka Volcanic Supergroup: Thoroughfare Creek and Sunlight Groups (Phanerozoic | Cenozoic | Tertiary | Eocene (44-49 Ma)): ABSAROKA VOLCANIC SUPERGROUP: THOROFARE CREEK GROUP (AGE 44 TO 49 Ma)--Light-colored volcaniclastic strata, andesite lava flows, and dark-brown breccia AND SUNLIGHT GROUP--including Trout Peak Trachyandesite, Wapiti Formation (andesitic volcaniclastic rocks), Crescent Hill Basalt, and Mount Wallace Formation (felsic and mafic volcaniclastic rocks).

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