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Geologic units containing volcanic breccia (agglomerate)

Arizona

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)

California

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 4 (Sierra Nevada) (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 4 (Sutter Buttes) (Quaternary (1.5-2.5 Ma))

Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.

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 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 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 14 (Tranquillon-Obispo) (Tertiary (16-18 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 1 (Quien Sabe-Burdell Mountain) (Tertiary (9.5-13 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.

Colorado

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Phanerozoic | Cenozoic | Tertiary)

Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences

Pre-ash-flow andesitic lavas, breccias, tuffs, and conglomerates (Phanerozoic | Cenozoic | Tertiary)

Includes several named units

Connecticut

Talcott Basalt (Lower Jurassic)

Talcott Basalt - Greenish-gray to black (weathers bright orange to brown), fine- to medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass. Pillows in many places; volcanic breccia with fragmentary pillows in others.

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.

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 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.

Rhyolitic domes, flows, pyroclastic debris, and basalt flows; Early Pleistocene subvolcanic to volcanic features; eastern Snake River Plain (Early Pleistocene)

Lower Pleistocene to Pliocene silicic volcanic units near the Snake Plain.

Trachyandesite, latite, trachybasalt flows, dikes, and volcaniclastic debris; Eocene intermediate volcanics; central Idaho, southern Challis volcanic field (Eocene)

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

Massachusetts

Hitchcock Volcanics (Lower Jurassic)

Hitchcock Volcanics - Nested cones of basaltic breccia containing abundant fragments of New Haven Arkose (Jn, TRn), locally intrusive into arkose near base; overlain by lava flow of Holyoke Basalt (Jhb) and/or Shuttle Meadow Formation (Jsm).

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).

Michigan

Basaltic and andesitic breccia (Early Proterozoic)

Basaltic and andesitic breccia - Exposed in northeastern Wisconsin

New Hampshire

Moat Volcanics (Middle Jurassic?)

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

Nevada

Breccia (Middle Eocene to Early Pliocene)

BRECCIA-Volcanic, thrust, and jasperoid breccia and landslide megabreccia

Oregon

Basaltic lava flows (Oligocene to Miocene)

Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palagonitic tuff and breccia

Basaltic lava flows (Oligocene to Miocene)

Basaltic and basaltic andesite lava flows and breccia; grades laterally into rare bedded palagonitic tuff and breccia

Fisher and Eugene Formations and correlative rocks (Oligocene and upper Eocene) (Late Eocene to Oligocene)

Thin to moderately thick bedded, coarse- to fine-grained arkosic and micaceous sandstone and siltstone, locally highly pumiceous, of the marine Eugene Formation; and coeval and older andesitic lapilli tuff, breccia, water-laid and air-fall silicic ash of the continental Fisher and Colestin Formations; upper parts of the Fisher Formation apparently lap onto and interfinger with the Eugene Formation. Megafauna in the Eugene Formation were assigned an Oligocene age by Vokes and others (1951) and foraminifers have been assigned to the upper part of the lower Refugian Stage (McDougall, 1980), or of late Eocene age. Basalt lava flows in the Fisher Formation have yielded isotopic ages as old as 40 Ma (Lux, 1982), and south of the latitude of Cottage Grove the Fisher is overlain by a welded tuff in unit Tu dated at about 35 Ma. North of Eugene, rocks of this unit are overlain unconformably by continental volcanogenic rocks of unit Tu, including an ash-flow tuff with a K-Ar age of 30.9 +/- 0.4 Ma

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

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

Siletz River Volcanics and related rocks (middle and lower Eocene and Paleocene) (Paleocene to Middle Eocene)

Aphanitic to porphyritic, vesicular pillow flows, tuff-breccias, massive lava flows and sills of tholeiitic and alkalic basalt. Upper part of sequence contains numerous interbeds of basaltic siltstone and sandstone, basaltic tuff, and locally derived basalt conglomerate. Rocks of unit pervasively zeolitized and veined with calcite. Most of these rocks are of marine origin and have been interpreted as oceanic crust and seamounts (Snavely and others, 1968). Foraminiferal assemblages referred to the Ulatisian and Penutian Stages (Snavely and others, 1969); K-Ar ages range from 50.7 +/- 3.1 to 58.1 +/- 1.5 Ma (Duncan, 1982); includes the lower part of the Roseburg Formation of Baldwin (1974), which has yielded K-Ar ages as old as 62 Ma

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)

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

Rhode Island

Scituate Igneous Suite - volcaniclastic rock (Devonian)

Scituate Igneous Suite - volcaniclastic rock - Dark-gray, pink, greenish, and purplish tuff and epiclastic rock (sandstone, breccia, conglomerate) containing abundant volcanic detritus. Tuff may include ignimbrite and ash-flow tuff. Fiamme common in some rock mapped formerly as Spencer Hill Volcanics.

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

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

Eagle Mountains caldera volcanic rocks

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

South Rim Formation from Pine Canyon Caldera

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

Van Horn Mountains caldera volcanic rocks

Wiley Mountain caldera volcanic rocks (Phanerozoic | Cenozoic | Tertiary | Eocene)

Wiley Mountain caldera volcanic rocks

Vermont

Ammonoosuc Volcanics (Ordovician)

Ammonoosuc Volcanics - Soda-rhyolite tuff, breccia, and flows. (Northeastern Vermont).

Volcanic breccia, felsitic tuff, and flows. (Permian-Triassic)

Volcanic breccia, felsitic tuff, and flows.

Washington

Cretaceous nonmarine rocks (Late Cretaceous)

Redbeds of thick-bedded sandstone, shale, and pebble conglomerate in upper Methow River area of Okanogan County.

Lower upper Eocene marine and nonmarine rocks (Eocene)

Predominantly massive to well-bedded tuffaceous marine siltstone with interbedded arkosic and basaltic sandstone. Includes conglomerate in King County and along north side of Olympic Peninsula. Minor lava flows and breccia in western Lewis County and eastern Grays Harbor County. Coal seams in central Lewis County and north-central Pierce County.

Oligocene volcanic rocks (Oligocene)

Andesite and rhyodacite flows, tuff, and tuffaceous sandstones of northern Lincoln County and southwestern Stevens County.

Tertiary nonmarine rocks, undivided (Tertiary; mostly Eocene)

Sandstone, shale, conglomerate, agglomerate, and tuff; includes some lava flows. Massive conglomerate, sandstone, siltstone, and ferruginous shale in northwestern Whatcom County.

Wisconsin

Basaltic and andesitic breccia (Early Proterozoic)

Basaltic and andesitic breccia - Exposed in northeastern Wisconsin