USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state

Geologic units containing rhyolite

Arizona

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 granitic rocks (Early Proterozoic)

Wide variety of granitic rocks, including granite, granodiorite, tonalite, quartz diorite, diorite, and gabbro. These rocks commonly are characterized by steep, northeast-striking foliation. (1600-1800 Ma)

Early Proterozoic metasedimentary rocks (Early Proterozoic)

Metasedimentary rocks, mostly derived from sandstone and shale, with minor conglomerate and carbonate rock. Includes quartz-rich, mostly nonvolcanic Pinal Schist in southeastern Arizona and variably volcanic-lithic sedimentary rocks in the Yavapai and Tonto Basin supergroups in central Arizona. (1600-1800 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 and Triassic sedimentary and volcanic rocks (Triassic and Jurassic)

Undivided massive quartz-feldspar porphyry of the Jurassic Planet Volcanics, quartz-rich metasandstone of the Jurassic Vampire Formation, and quartzite, phyllite, and fine grained, variably calcareous metasiltstone of the Triassic Buckskin Formation; exposed primarily in the Buckskin and Rawhide Mountains of western Arizona. This unit also includes sandstone and conglomerate beneath Jurassic volcanic rocks in the central Dome Rock Mountains. (160-240 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)

Jurassic to Cambrian metamorphosed sedimentary rocks (Cambrian to Jurassic)

Highly faulted and folded rocks of units Jv, J_, and Pz, deformed and metamorphosed in Jurassic, Cretaceous and Tertiary time. This unit is restricted to west-central Arizona. (160-540 Ma)

Jurassic volcanic rocks (Jurassic)

Massive quartz-feldspar porphyry, generally interpreted as thick, welded rhyolitic tuffs, with locally abundant lava, and sandstone and conglomerate derived from volcanic rocks. Rare eolian quartzite units are interbedded in southern Arizona. Includes Ali Molina Formation, Mount Wrightson Formation, part of the Canelo Hills Volcanics, Cobre Ridge tuff, Black Rock volcanics, Planet Volcanics, and equivalent rocks. (160-200 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 shallow intrusions (Oligocene to Middle Miocene)

Generally very fine-grained, porphyritic rhyolite to dacite in small, irregular-shaped bodies formed as subvolcanic intrusions in volcanic fields of southern and western Arizona, or in concentrated zones of dikes in the Mohave and Black Mountains of northwestern Arizona. The unit consists of mafic tuff, breccia and shallow intrusions at Buell Park in northeastern Arizona. (14-35 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

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 2 (Long Valley Caldera) (Quaternary (0-1 Ma))

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 pyroclastic and volcanic mudflow deposits, unit 5 (Coso Volcanic Field) (Quaternary)

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 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.

Recent (Holocene) pyroclastic and volcanic mudflow deposits, unit 2 (Mono Craters) (Holocene)

Recent (Holocene) pyroclastic and volcanic mudflow deposits; in part Pleistocene.

Recent (Holocene) volcanic flow rocks, unit 2 (Mono Craters) (Holocene)

Recent (Holocene) volcanic flow rocks; minor pyroclastic deposits; in part Pleistocene.

Recent (Holocene) volcanic flow units, unit 5 (Salton Sea) (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 3 (Pinnacles Volcanic Field) (Tertiary)

Tertiary intrusive rocks; mostly shallow (hypabyssal) plugs and dikes. Includes some Mesozoic rocks.

Tertiary intrusive rocks (hypabyssal), unit 4 (Tranquillon-Obispo) (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 intrusive rocks (hypabyssal), unit 7 (Northern 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 2 (Berkeley Hills) (Tertiary (8-12 Ma))

Tertiary pyroclastic and volcanic mudflow deposits.

Tertiary pyroclastic and volcanic mudflow deposits, unit 3 (Pinnacles-Neenach) (Tertiary (22-24 Ma))

Tertiary pyroclastic and volcanic mudflow deposits.

Tertiary pyroclastic and volcanic mudflow deposits, unit 4 (Tranquillon-Obispo) (Tertiary (16-18 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 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 12 (Sam Emigdio) (Tertiary (22-25 Ma))

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Tertiary volcanic flow rocks, unit 14 (Tranquillon-Obispo) (Tertiary (16-18 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 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 4 (Berkeley Hills) (Tertiary (8-12 Ma))

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Colorado

Rhyolitic intrusive rocks and flows of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary)

Connecticut

Porphyry (dacite or rhyolite) (Permian)

Porphyry (dacite or rhyolite) - Light-colored, very fine grained, massive porphyry with phenocrysts of quartz, feldspar, and biotite; muscovite and accessory fluorite in groundmass.

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.

Metavolcanic and metasedimentary rocks; Jurassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex (Jurassic)

Jurassic mixed marine detrital and volcanic rocks of western Idaho.

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 dikes and plugs; Miocene felsic subvolcanic feeder intrusions; Owyhee Plateau (Tertiary)

Tertiary intrusive rock; where adequately dated, intrusions are denoted (Tmi, Tei).

Rhyolite flows and ignimbrites; Late Pleistocene felsic volcanics of subunit 3f; Yellowstone Plateau (Late Pleistocene)

Upper Pleistocene silicic volcanic unit 3 in eastern Idaho.

Rhyolite flows and ignimbrites; Late Pleistocene felsic volcanics; Yellowstone Plateau (subunits are Qpu1f and Qpu2f) (Late Pleistocene)

Upper Pleistocene silicic volcanic units; in eastern Idaho subdivisions are (Qpu3f, Qpu2f, Qpu1f)

Rhyolite flows; Late Pleistocene rhyolite lava flows of subunit 1f; Yellowstone Plateau (Late Pleistocene)

Upper Pleistocene silicic volcanic unit 1 in eastern Idaho.

Rhyolite flows; Middle Pleistocene felsic volcanics of subunit 1f; eastern Snake River Plain and Yellowstone Plateau (Middle Pleistocene)

Middle Pleistocene silicic volcanic unit 1 in eastern 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.

Rhyolite ignimbrites; Early Pleistocene felsic volcanics; Yellowstone Plateau (Early Pleistocene)

Lower Pleistocene silicic volcanic units of the Island Park-Yellowstone area.

Rhyolite ignimbrites; Late Pleistocene felsic volcanics of subunit 2f; Yellowstone Plateau (Late Pleistocene)

Upper Pleistocene silicic volcanic unit 2 in eastern Idaho.

Rhyolite ignimbrites, latite and basalt lava flows, late Eocene rhyolitic ignimbrite cauldron complex; east-central Idaho, northern Challis volcanic field (Eocene)

Eocene mixed silicic and basaltic volcanic ejecta, flows and reworked debris.

Rhyolite ignimbrites; Middle Pleistocene felsic volcanics of subunit 2f; Yellowstone Plateau (Middle Pleistocene)

Middle Pleistocene silicic volcanic unit 2 in eastern Idaho.

Rhyolite ot trachyte ignimbrites and flows; Pliocene felsic volcanics; eastern Snake River Plain and vicinity (Pliocene)

Pliocene silicic welded tuff, ash, and flow rock; most common in southwestern Idaho.

Rhyolite, quartz latite, and latite ignimbrites and flows; Miocene felsic volcanics; Owyhee Plateau; (Miocene)

Miocene silicic flows, tuffs; most common in southwestern Idaho.

Rhyolitic tuffs, ignimbrites, and flows, basaltic flows, conglomerate and marlstone; Pliocene to Miocene volcano-sedimentary deposits; eastern Snake River Plain and southeastern Idaho (Pliocene-Miocene)

Pliocene volcanic units, generally air-fall or pyroclastic in origin; grade into (Tpd).

Shale, arenite, conglomerate, intermediate and felsic volcanic rocks; Late Proterozoic rifted continental margin; southeastern Idaho (Late Proterozoic)

Younger Precambrian volcanic and diamictic units of central and southeastern Idaho.

Massachusetts

Lynn Volcanic Complex (Lower Devonian, Silurian, or Proterozoic Z)

Lynn Volcanic Complex - Rhyolite, agglomerate and tuff.

Mattapan Volcanic Complex (Proterozoic Z or younger)

Mattapan Volcanic Complex - Rhyolite, melaphyre, agglomerate, and tuff. Mattapan Volcanic Complex is found in west and southwest part of Boston basin and beyond, and to the south in Blue Hills. Similar in lithology to Lynn Volcanic Complex. Both units consist largely of partly porphyritic rhyolite and rhyodacite flows, welded ash-flow tuffs, vitric tuff, lapilli tuff, lithic tuff, flow breccias, breccia pipes, and extrusion domes. Mattapan's rhyolite and rhyodacites are thinner and less varied in composition and texture than Lynn's, and volcanic breccias are absent in Lynn. Both units are reported to lie nonconformably on Dedham Granite and unnamed plutonic-volcanic complex of eastern MA; however, Mattapan has been observed as dikes and stocks cutting Dedham Granite (Billings, 1976; Kaye and Zartman, 1980; Chute, 1966), and other workers have pointed out evidence that some of Mattapan may be penecontemporaneous with younger phases of Dedham batholith. Westwood Granite may be intrusive equivalent of Mattapan. Mattapan is conformably and fairly continuously overlain by Roxbury Conglomerate of Boston Bay Group. LaForge (19832) cautioned against identifying rocks interbedded within Mattapan that look like Roxbury, but are still part of Mattapan. Metavolcanic rocks in Blue Hills resembling Mattapan are assigned to Mattapan on State bedrock map (Zen and others, 1983); for years they were considered to be either Silurian and Devonian, or Carboniferous; however, they are chemically and mineralogically distinct from Ordovician and Silurian Blue Hills [sic] Granite Porphyry. Author follows usage of Chute (1966) who could find no difference between volcanic rocks in Blue Hills area and Mattapan rocks, and thus these rocks are assigned to Mattapan. Proterozoic Z age is based on U-Th-Pb zircon date of 602 +/-3 Ma (Zartman, in Kaye and Zartman, 1980). Although Billings (1979) questions reliability of zircon ages from volcanic rocks, discovery of Proterozoic Z acritarchs in overlying Cambridge Argillite indicates zircon age is appropriate (Goldsmith, 1991).

Newbury Volcanic Complex (Lower Devonian and Upper Silurian)

Newbury Volcanic Complex - Micrographic rhyolite, intrudes DSnu, DSna, DSnl.

Newbury Volcanic Complex (Lower Devonian and Upper Silurian)

Newbury Volcanic Complex - Lower members. Basalt, andesite, rhyolite, and tuff.

Wamsutta Formation (Middle and Lower Pennsylvanian)

Wamsutta Formation - Rhyolite and mafic volcanic rocks in the Wamsutta Formation. Wamsutta Formation occurs in Narragansett and Norfolk basins. Consists of conglomerate, lithic graywacke, sandstone, and shale. Also contains rhyolite and basalt horizons near Attleboro. Northwest of Attleboro, Wamsutta overlies Diamond Hill Felsite as used by Skehan and Murray (in Skehan and others, 1979). Volcanic rocks similar to Diamond Hill Felsite crop out west of Lake Pearl, between Franklin and Wrentham, on west flank of Norfolk basin. These are shown within Wamsutta Formation on MA State bedrock map of Zen and others (1983) because of their proximity to Diamond Hill. They also resemble Proterozoic Z Mattapan Volcanic Complex. Chute (1966) described lenses of carbonate rock in red and green shale in Wamsutta in Norwood quad. Limestone also observed in rocks mapped as Wamsutta adjacent to exposed Dedham Granite at Manchester Pond Reservoir (J.P. Schafer, 1982, oral commun.). Red and green shales may actually be Cambrian. Upper member of Pondville Conglomerate grades into and interfingers with Wamsutta; in turn, Wamsutta interfingers with Rhode Island Formation in northwest part of Narragansett basin. Nonconformably overlies Dedham Granite. Partly equivalent to Rhode Island Formation. Age is Early and Middle Pennsylvanian. Contains a few plant fossils (Goldsmith, 1991).

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

Cambrian Hurricane Mountain Formation, metafelsite (Cambrian)

Cambrian Hurricane Mountain Formation, metafelsite

Devonian Heald Mountain Rhyolite (Devonian)

Devonian Heald Mountain Rhyolite

Devonian Heald Mountain Rhyolite dark tuff member (Devonian)

Devonian Heald Mountain Rhyolite dark tuff member

Devonian - Silurian Vinalhaven Rhyolite (Devonian - Silurian)

Devonian - Silurian Vinalhaven Rhyolite

Devonian Tomhegan Formation Kineo Rhyolite member garnet rhyolite (Devonian)

Devonian Tomhegan Formation Kineo Rhyolite member garnet rhyolite

Devonian Tomhegan Formation Kineo Rhyolite member tuffs and volcaniclastic rocks (Devonian)

Devonian Tomhegan Formation Kineo Rhyolite member tuffs and volcaniclastic rocks

Devonian Traveler Rhyolite Pogy member (Devonian)

Devonian Traveler Rhyolite Pogy member

Devonian unnamed garnet rhyolite (Devonian)

Devonian unnamed garnet rhyolite

Devonian unnamed rhyolite (Devonian)

Devonian unnamed rhyolite

Ordovician Bluffer Pond Formation rhyolite member (Ordovician)

Ordovician Bluffer Pond Formation rhyolite member

Ordovician Kennebec Formation (Ordovician)

Ordovician Kennebec Formation

Ordovician Quimby formation rhyolitic volcanic member (Ordovician)

Ordovician Quimby formation rhyolitic volcanic member

Ordovician Shin Brook Formation (Ordovician)

Ordovician Shin Brook Formation

Precambrian Z rocks of Islesboro (Precambrian Z)

Precambrian Z rocks of Islesboro

Tomhegan Formation, Kineo Rhyolite Member, Massive Felsite (Devonian)

Tomhegan Formation, Kineo Rhyolite Member, Massive Felsite

Traveler Rhyolite, Black Cat Member (Devonian)

Traveler Rhyolite, Black Cat Member

Michigan

Porcupine Volcanics (Middle Proterozoic)

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks

Porcupine Volcanics; Rhyolite (Middle Proterozoic)

Porcupine Volcanics; Rhyolite

Portage Lake Volcanics (Middle Proterozoic)

Portage Lake Volcanics - Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Portage Lake Volcanics; Rhyolite at Bergland (Middle Proterozoic)

Portage Lake Volcanics; Rhyolite at Bergland

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; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic)

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Minnesota

Chengwatana Volcanic Group (Middle Proterozoic)

Chengwatana Volcanic Group - Basalt and related volcanogenic and interflow sedimentary rocks in east-central Minnesota

North Shore Volcanic Group; Normally polarized volcanic rocks, undivided (Middle Proterozoic)

North Shore Volcanic Group; Normally polarized volcanic rocks, undivided - Basalt, andesitic basalt, rhyolite and related volcanogenic interflow sedimentary rocks along and inland from the North Shore of Lake Superior.

North Shore Volcanic Group; Reversely polarized volcanic rocks, undivided (Middle Proterozoic)

North Shore Volcanic Group; Reversely polarized volcanic rocks, undivided - Mixed tholeiitic diabasic and porphyritic basalt, trachybasalt, and rhyolite in far northeastern Minnesota and porphyritic and diabasic basalt near Duluth. Includes units of a basal quartz arenite, Puckwunge Sandstone and Nopeming Formation, in northeastern Minnesota and near Duluth, respectively.

Missouri

ST. FRANCOIS MOUNTAINS VOLCANIC SUPERGROUP (Precambrian [Y])

ST. FRANCOIS MOUNTAINS VOLCANIC SUPERGROUP (chiefly alkali rhyolitic ash - flow tuffs, lava flows, and bedded tuffs, with minor trachytes.

North Carolina

Mount Rogers Formation; Metagraywacke (Late Proterozoic)

Metagraywacke - interlayered with metaconglomerate, laminated metasiltstone, and slate; minor calcareous metasandstone, greenstone, and metarhyolite.

Rhyolite (Jurassic)

Rhyolite (196 my) - dike, medium to dark gray, phenocrysts of sanidine, anorthoclase, and quartz; commonly with calcite or clay amygdules.

Rhyolite (Jurassic)

Rhyolite (196 my) - dike, medium to dark gray, phenocrysts of sanidine, anorthoclase, and quartz; commonly with calcite or clay amygdules.

New Hampshire

Moat Volcanics (Middle Jurassic?)

Moat Volcanics - Bedded and ignimbritic tuffs, flows, and breccias; also porphyritic rhyolite and minor trachyte.

Rhyolite and fine-grained granite (Cretaceous)

Rhyolite and fine-grained granite - Includes some ignimbritic caldera-fill and minor intrusive rocks (part of Ossipee Mountain Complex of Kingsley, 1931); also some aphanitic gray, black, or tan quartz-feldspar porphyry.

New Jersey

Chestnut Hill Formation (Late Proterozoic)

Chestnut Hill Formation (Drake, 1984) - Interbedded arkose, ferruginous quartzite, quartzite conglomerate, metarhyolite, and metasaprolite. Confined to a few small areas north and east of Phillipsburg, on the western side of Bowling Green Mountain, northwest of High Bridge, and a few areas too small to show at this map scale.

New Mexico

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

Bandelier Tuff (Phanerozoic | Cenozoic | Quaternary)

Bandelier Tuff; Jemez Mountains area only

felsic shallow-intrusive rocks (Phanerozoic | Cenozoic | Tertiary)

Middle Tertiary felsic shallow-intrusive rocks; phonolites and trachytes of northeastern N.M.; includes the rhyolite of Ash Mountain

Hinsdale Basalt (Phanerozoic | Cenozoic | Tertiary)

Hinsdale Basalt; northern Taos and eastern Rio Arriba Counties; basalt flows interbedded with Los Pinos Formation

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)

silicic flows and massess and associated pyroclastic rocks (Phanerozoic | Cenozoic | Tertiary)

Upper Oligocene silicic (or felsic) flows and masses and associated pyroclastic rocks; includes Taylor Creek, Fanney, and Rocky Canyon Rhyolites

Valles Rhyolite (Phanerozoic | Cenozoic | Quaternary)

Valles Rhyolite; Jemez Mountains area only

Nevada

Ash-flow tuffs and tuffaceous sedimentary rocks (Middle Miocene to Late Miocene)

ASH-FLOW TUFFS AND TUFFACEOUS SEDIMENTARY ROCKS

Ash-flow tuffs, rhyolitic flows, and shallow intrusive rocks (Middle Miocene to Late Miocene)

ASH-FLOW TUFFS, RHYOLITIC FLOWS, AND SHALLOW INTRUSIVE ROCKS

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

Leucogranite and rhyolite porphyry (Mississippian to Triassic)

LEUCOGRANITE AND RHYOLITE PORPHYRY

Rhyolitic flows and shallow intrusive rocks (Miocene to Quaternary)

RHYOLITIC FLOWS AND SHALLOW INTRUSIVE ROCKS

Rhyolitic flows and shallow intrusive rocks (Early Oligocene to Early Miocene)

RHYOLITIC FLOWS AND SHALLOW INTRUSIVE ROCKS

Rhyolitic flows and shallow intrusive rocks (Middle Miocene to Late Miocene)

RHYOLITIC FLOWS AND SHALLOW INTRUSIVE ROCKS

Rhyolitic flows and shallow intrusive rocks (Late Eocene to Middle Eocene)

RHYOLITIC FLOWS AND SHALLOW INTRUSIVE ROCKS

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 sandstone, felsic ash-flow tuffs, rhyolite, and rhyodacite flows (Middle Jurassic to Early Cretaceous)

VOLCANIC SANDSTONE, FELSIC ASH-FLOW TUFFS, RHYOLITE, AND RHYODACITE FLOWS (Upper? Jurassic)-Pony Trail Group of Cortez Mountains, Eureka County

Welded and nonwelded silicic ash-flow tuffs (Late Eocene to Middle Eocene)

WELDED AND NONWELDED SILICIC ASH-FLOW TUFFS-Locally includes thin units of air-fall tuff and sedimentary rock

Welded and nonwelded silicic ash-flow tuffs (Middle Miocene to Late Miocene)

WELDED AND NONWELDED SILICIC ASH-FLOW TUFFS-Locally includes thin units of air-fall tuff and sedimentary rock

Welded and nonwelded silicic ash-flow tuffs (Early Oligocene to Early Miocene)

WELDED AND NONWELDED SILICIC ASH-FLOW TUFFS-Locally includes thin units of air-fall tuff and sedimentary rock

New York

Lamprophyre, trachyte, and rhyolite dikes (Jurassic - Lower Cretaceous)

Lamprophyre, trachyte, and rhyolite dikes - not shown in Proterozoic terrane.

Oklahoma

Carlton Rhyolite Group (Phanerozoic | Paleozoic | Cambrian-Middle)

CLINTON- Rhyolite flows and tuffs; about 4,500 feet thick; one outlier is shown in southern part of mapped area. LAWTON- Rhyolite flows, tuffs, conglomerate beds, and diabase sills; thickness, 4,500 feet (1,370 m).

Colbert Porphyry (Phanerozoic | Paleozoic | Cambrian-Middle)

ARDMORE-SHERMAN- Rhyolite porphyry, red-brown, flow-banded; thickness, 7,500 feet. Probably rests on 7,500 feet of metasedimentary and basaltic rocks in geosynclinal province of western Arbuckle Mountains. (525 million years old) Occurs in the ARBUCKLE MTNS

Spavinaw Granite (Phanerozoic | Paleozoic | Cambrian-Middle)

TULSA- no description given

Oregon

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

Rhyolite and dacite domes and flows and small hypabyssal intrusive bodies (Miocene to upper Eocene?) (Late Eocene to Miocene)

Mostly light-gray to red, dense, flow-banded, nonporphyritic and porphyritic rhyolite and dacite in nested domes, small intrusive bodies, and related flows. Includes some near-vent breccias, pumice-lapilli tuffs, and coarse pumicites. Commonly associated with mercury mineralization. Includes several small hypabyssal intrusions of diorite, granodiorite, and quartz monzonite exposed in Paisley Hills of Lake County (Muntzert, 1969; Muntzert and Field, 1968). In many places represents vents for lava flows and tuff of unit Tsf

Rhyolite and dacite (Holocene and Pleistocene) (Pleistocene to Holocene)

Domes and related flows and flow breccia of aphyric and plagioclase and hornblende porphyritic rhyolite and dacite. Includes rhyolite and dacite on Newberry volcano and at South Sister volcano in the Cascade Range that are younger than Mazama ash deposits (Qma , Qmp; radiometrically dated by 14C methods at approximately 6,800 yr old)

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

Silicic ash-flow tuff (lower Pliocene and upper Miocene) (Late Miocene to Early Pliocene)

Ash-flow tuff and associated pumiceous air-fall tuff mostly of rhyolitic and rhyodacitic composition; includes minor tuffaceous sedimentary rocks. Grades laterally through less-densely welded tuff to nonwelded ash-flow tuff and interlayered tuffaceous sediments of unit Ts. Potassium-argon ages (Greene and others, 1972; Parker and Armstrong, 1972; Walker, 1979; McKee and others, 1976) on several different ash-flow tuffs included in unit range from about 4 to 10 Ma; although most ages are in the range of 6 to 9 Ma. Includes the Devine Canyon, Prater Creek, and Rattlesnake Ash-flow Tuffs (Walker, 1979), originally considered a part of the (now obsolete) Danforth Formation of Piper and others (1939), and the Rattlesnake Formation and the volcanic and fluvial deposits (undivided) and marginal facies of the Columbia River Group (undivided) of Brown and Thayer (1966). Also includes the welded soda--rhyolite tuff breccia of Dickinson and Vigrass (1965) in the Suplee-Izee area, the upper Miocene or lower Pliocene welded tuff of Prostka (1962; 1967) in the Baker area. "Welded ash-flow tuff" of Swanson (1969a) and the Pliocene Peyerl Tuff (Hampton, 1964) west of Fort Rock Valley, dated at about 4.5 Ma (McKee and others, 1976)

Silicic vent complexes (Pliocene, Miocene, and upper Oligocene) (Miocene)

Large, rhyolitic to dacitic vent areas in the Cascade Range that commonly include multiple intrusions and much associated silicic eruptive breccia and erosional debris and some flows

Silicic vent deposits (Pleistocene and Pliocene) (Pliocene to Pleistocene)

Complex domal masses of rhyolite and dacite that include near-vent flows, breccia, pumicite, perlite, obsidian, and ash-flow tuff

Silicic vent rocks (Pliocene, Miocene, Oligocene, and Eocene?) (Eocene to Pliocene)

Plugs and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; includes related near-vent flows, flow breccia, and deposits of obsidian, perlite, and pumice. Locally includes resurgent domes related to caldera complexes. In southeast Oregon many domal complexes younger than 11 Ma exhibit a well-defined southeast to northwest age progression (Walker, 1974; MacLeod and others, 1976) from about 11 Ma to less than 1 Ma

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)

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

Tuffaceous sedimentary rocks, tuffs, pumicites, and silicic flows (Miocene) (Miocene)

Moderately well indurated lacustrine and fluvial (flood-plain) deposits of tuff, pumicite, palagonite tuff, and lesser siltstone, arkosic sandstone, and pebble and cobble conglomerate. Locally contains some lignite beds. Former glass in silicic vitroclastic debris commonly crystallized and altered to secondary silica minerals, alkali feldspar, zeolites, and clay minerals. Contains some welded and nonwelded ash-flow tuffs, and minor rhyolite flows. Widespread and abundant vertebrate fossils and minor plant fossils indicate that most of unit is of middle Miocene (Barstovian) age; parts of unit between Goose Lake and Warner Valley may include rocks of early Miocene age. Locally interlayered with and locally overlies basalt and andesite flows of unit Tmb. Overlies and locally interfingers with Picture Gorge Basalt (Thayer and Brown, 1966) and with Miocene basalt south of Prineville. Includes Mascall Formation of Merriam (1901), Sucker (Succor) Creek Formation of Corcoran and others (1962) and Kittleman and others (1967), Drip Spring Formation of Kittleman and others (1965, 1967), Trout Creek Formation of Smith (1926), and "rocks of Miocene age" of Malde and Powers (1962) in the southern Owyhee Upland province. In southeast Oregon, some of these rocks represent caldera and moat-fill deposits

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

Welded tuffs and tuffaceous sedimentary rocks (upper? and middle Miocene) (Middle to Late Miocene)

Partly to densely welded vitric and vitric-crystal tuff of soda-rhyolitic, rhyolitic, and rhyodacitic composition that interfingers with and grades laterally into unit Tit. Includes some nonwelded ash-flow tuff and tuffaceous sedimentary rocks. Potassium-argon ages range from about 13 to 16 Ma. In Harney and Malheur Counties, it commonly overlies unit Tmb. Includes Dinner Creek Welded Tuff of Haddock (1965; 1967) and middle and upper Miocene ash-flow tuffs of Rytuba and others (1982; 1983a, b), widely exposed in the Trout Creek Mountains and adjacent areas, erupted from the McDermitt caldera complex, west and southwest of McDermitt, Nevada-Oregon, the White Horse caldera, northwest of McDermitt, and several other vent areas

Welded tuffs and tuffaceous sedimentary rocks (upper? and middle Miocene) (Middle to Late Miocene)

Partly to densely welded vitric and vitric-crystal tuff of soda-rhyolitic, rhyolitic, and rhyodacitic composition that interfingers with and grades laterally into unit Tit. Includes some nonwelded ash-flow tuff and tuffaceous sedimentary rocks. Potassium-argon ages range from about 13 to 16 Ma. In Harney and Malheur Counties, it commonly overlies unit Tmb. Includes Dinner Creek Welded Tuff of Haddock (1965; 1967) and middle and upper Miocene ash-flow tuffs of Rytuba and others (1982; 1983a, b), widely exposed in the Trout Creek Mountains and adjacent areas, erupted from the McDermitt caldera complex, west and southwest of McDermitt, Nevada-Oregon, the White Horse caldera, northwest of McDermitt, and several other vent areas

Rhode Island

Scituate Igneous Suite - rhyolite (Devonian)

Scituate Igneous Suite - rhyolite - Pink to gray, fine-grained, locally porphyritic felsite (phenocrysts of quartz and Carlsbad-twinned orthoclase). Includes some hypabyssal intrusive rocks (feeder dikes and sills), and some probable lava flows. Contains accessory biotite, opaque minerals, zircon, monzonite, fluorite, sphene, apatite, and epidote. Quartz phenocrysts commonly are embayed and partly resorbed; matrix is fine-grained intergrowth of quartz and feldspar, probably formed from devitrified glass. Includes some rock mapped formerly as Spencer Hill Volcanics and Maskerchugg Granite.

South Dakota

Rhyolitic Intrusive Rocks (Phanerozoic | Cenozoic | Tertiary | Paleocene Eocene)

Light-tan to light-gray stocks and small laccoliths of rhyolite. Contains phenocrysts of oligoclase, quartz, and biotite in a finely crystalline orthoclase or sanidine-quartz groundmass.

Trachytic Intrusive Rocks (Phanerozoic | Cenozoic | Tertiary | Paleocene Eocene)

Tan to reddish-brown, iron-stained stocks, laccoliths, sills, and dikes of trachyte, quartz trachyte, and alkalic rhyolite. Contains phenocrysts of sanidine, orrthoclase, anorthoclase, aegirine-augite and biotite in a finely crystalline orthoclase-quartz biotite groundmass.

Texas

Bofecillos volcano volcanic rocks, including units 1-8 of Rawls Formation and lava flows in upper part of Fresno Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene)

Bofecillos volcano volcanic rocks, including units 1-8 of Rawls Formation and lava flows in upper part of Fresno Formation

Carrizo Mountain Group showing metaigneous rocks (preCambrian-Proterozoic)

Carrizo Mountain Group showing metaigneous rocks

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

Duff Formation, Decie Member from Paisano caldera (Phanerozoic | Cenozoic | Tertiary | Oligocene-Early)

Duff Formation, Decie Member from Paisano caldera

Duff Formation (with Decie Member from Paisano caldera shown separately), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided (Phanerozoic | Cenozoic | Tertiary | Eocene-Late Oligocene-Early)

Duff Formation (with Decie Member from Paisano caldera shown separaetly), Cottonwood Springs Basalt, Potato Hill Andesite, Sheep Canyon Basalt, Crossen Trachyte, and Pruett Formation, undivided

Eagle Mountains caldera volcanic rocks (Phanerozoic | Cenozoic | Tertiary | Oligocene)

Eagle Mountains caldera volcanic rocks

Eocene intrusive rocks (Phanerozoic | Cenozoic | Tertiary | Eocene)

Eocene intrusive rocks

Eocene volcanic rocks (Phanerozoic | Cenozoic | Tertiary | Eocene)

Eocene volcanic 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

older volcanic rocks of Davis and Barilla Mountains, including Sheep Pasture, Sleeping Lion, Frazier Canyon, Adobe Canyon, and Limpia formations, Gomez Tuff, Star Mountain Rhyolite, and Huelster Formation (Phanerozoic | Cenozoic | Tertiary | Eocene-Late)

older volcanic rocks of Davis and Barilla Mountains, including Sheep Pasture, Sleeping Lion, Frazier Canyon, Adobe Canyon, and Limpia formations, Gomez Tuff, Star Mountain Rhyolite, and Huelster Formation

Oligocene intrusive rocks (Phanerozoic | Cenozoic | Tertiary | Oligocene)

Oligocene intrusive rocks

Quitman Mountains caldera volcanic rocks and volcanic rocks of sneed (Cox) Mountain and west of Victorio Peak (Phanerozoic | Cenozoic | Tertiary | Oligocene)

Quitman Mountains caldera volcanic rocks and volcanic rocks of sneed (Cox) Mountain and west of Victoria Peak

Rhyolite (preCambrian-Proterozoic [Grenville])

Rhyolite

South Rim Formation from Pine Canyon Caldera (Phanerozoic | Cenozoic | Tertiary | Oligocene)

South Rim Formation from Pine Canyon Caldera

upper part of Shely Group, including Tm4 or Morita Ranch Formation (Phanerozoic | Cenozoic | Tertiary | Oligocene)

upper part of Shely Group, including Tm4 or Morita Ranch Formation

Van Horn Mountains caldera volcanic rocks (Phanerozoic | Cenozoic | Tertiary | Eocene)

Van Horn Mountains caldera volcanic rocks

Vieja Group, including Bracks Rhyolite, Chambers and Colmena Tuffs and Gill Breccia (Phanerozoic | Cenozoic | Tertiary | Eocene Oligocene)

Vieja Group, including Bracks Rhyolite, Chambers and Colmena Tuffs and Gill Breccia

younger volcanic rocks of Davis Mountains area including Brooks Mountain, Goat Canyon, Medley, Barrel Springs, Wild Cherry, Eppenaurer Ranch, Mount Locke, and Merrill Formations (Phanerozoic | Cenozoic | Tertiary | Oligocene-Early)

younger volcanic rocks of Davis Mountains area including Brooks Mountain, Goat Canyon, Medley, Barrel Springs, Wild Cherry, Eppenaurer Ranch, Mount Locke, and Merrill Formations

Utah

Miocene rhyolites (Middle to Late Miocene)

Oligocene volcanic rocks (Late Eocene to Oligocene)

Pliocene basalts (Pliocene)

Pliocene rhyolites (Pliocene)

Quaternary basalts (Quaternary)

Quaternary rhyolites (Quaternary)

Virginia

Catoctin Formation - Metarhyolite (Proterozoic Z-Cambrian)

Catoctin Formation- Metarhyolite

Mount Rogers Formation - Conglomerate, graywacke, laminated siltstone, and shale. (Proterozoic Z)

Mount Rogers Formation - Conglomerate, graywacke, laminated siltstone, and shale.

Mount Rogers Formation - Phenocryst-poor rhyolite (Proterozoic Z)

Mount Rogers Formation - Phenocryst-poor rhyolite

Mount Rogers Formation - Porphyritic rhyolite (Proterozoic Z)

Mount Rogers Formation - Porphyritic rhyolite

Washington

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.

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.

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.

Pleistocene-Recent volcanic rocks (Pleistocene to Holocene)

Predominantly dark-gray to black vesicular basalt; olivine-rich in part. Includes andesite flows and pyroclastic rocks of Mount Baker, Glacier Peak, Mount Rainier, Mount Adams, Mount St. Helens, and all cinder cones in southern part of the State. Also includes some Recent flows southeast of Mount St. Helens.

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-Middle Eocene)

Rhyolite flows and some interbedded tuff beds in Cle Elum area, Kittitas County.

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 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)

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; Kallander Creek Volcanics; Upper rhyolite member (Middle Proterozoic)

Powder Mill Group; Kallander Creek Volcanics; Upper rhyolite member

Rhyolite (Early Proterozoic)

Rhyolite - Ash-flow tuffs and interbedded volcaniclastic sedimentary rocks and cogenetic granite (unit Xga) exposed as inliers in southern Wisconsin. In central Wisconsin pink, flow-banded rhyolite and chert-cemented breccia inferred to be 1760 Ma.

Rhyolite at and near Cary Mound and near Brokaw (about 1835 Ma) (Early Proterozoic)

Rhyolite at and near Cary Mound and near Brokaw (about 1835 Ma) - Flow-banded rhyolite, welded tuff, volcanic conglomerate, and volcanogenic sedimentary rocks. Exposed in both Pembine-Wausau and Marshfield terranes.

Wolf River batholith (1470 Ma); Hager Formation; Rhyolite member (Middle Proterozoic)

Wolf River batholith (1470 Ma); Hager Formation; Rhyolite member- Gray to reddish-gray, slightly foliated, porphyritic rhyolite containing aligned phenocrysts of alkali feldspar and lesser amounts of plagioclase in a fine-grained matrix of feldspar, biotite, amphibole, and sparse quartz

Wyoming

Conant Creek Tuff (Phanerozoic | Cenozoic | Tertiary | Miocene)

CONANT CREEK TUFF (AGE ABOUT 5.8 Ma)--Lavender rhyolite welded tuff.

Huckleberry Ridge Tuff of Yellowstone Group (Phanerozoic | Cenozoic | Tertiary | Pliocene)

HUCKLEBERRY RIDGE TUFF OF YELLOWSTONE GROUP (AGE SLIGHTLY MORE THAN 2 Ma)--Lavender to gray-brown welded rhyolite tuff.

Rhyolite flows, tuff, and intrusive igneous rocks (Phanerozoic | Cenozoic | Quaternary | Pleistocene)

RHYOLITE FLOWS, TUFF, AND INTRUSIVE IGNEOUS ROCKS--Includes Plateau Rhyolite (age about 0.07 Ma) and interlayered sediments, Mount Jackson Rhyolite (age 0.6 to about 1 Ma), Lewis Canyon Rhyolite (age about 0.9 Ma); and Lava Creek Tuff of Yellowstone Group (age 0.6 to about 1 Ma).

Rhyolite to diabase porphyry dikes (Proterozoic | Mesoproterozoic)

RHYOLITE TO DIABASE PORPHYRY DIKES (1,400 Ma).