EáuNSACLASSNLABELCNAMECEAGEC+DESCRIPTIOCþSOURCESCþ 100 Qs Surficial deposits, undivided Quaternary Unconsolidated beach, eolian, delta, lagoon, landslide, glacial, and alluvial deposits composed of silt, sand, gravel, and boulder-sized material. Primary and reworked pyroclastic material is a common component. In many locations, this deposit includesWilson, F.H., Mohadjer, Solmaz, and Grey, D.M., in press, Reconnaissance geologic map of the Western Aleutian Islands, Alaska - Integrated geologic map databases of the United States: U.S. Geological Survey Scientific Investigations Map SIM-XXXX, scales 105 Qa Alluvium Quaternary Sand, gravel, and silt including reworked cinders and ash. Includes old beach deposits in lower parts of some valleys on Attu and northern Adak Islands (Gates and others, 1971; Waythomas, 1995) as well as alluvial terrace deposits in low benches and unp 110 Qa Alluvium Quaternary Sand, gravel, and silt including reworked cinders and ash. Includes old beach deposits in lower parts of some valleys on Attu and northern Adak Islands (Gates and others, 1971; Waythomas, 1995) as well as alluvial terrace deposits in low benches and unp 170 Qa Alluvium Quaternary Sand, gravel, and silt including reworked cinders and ash. Includes old beach deposits in lower parts of some valleys on Attu and northern Adak Islands (Gates and others, 1971; Waythomas, 1995) as well as alluvial terrace deposits in low benches and unp 116 Qs Surficial deposits, undivided Quaternary Unconsolidated beach, eolian, delta, lagoon, landslide, glacial, and alluvial deposits composed of silt, sand, gravel, and boulder-sized material. Primary and reworked pyroclastic material is a common component. In many locations, this deposit includesWilson, F.H., Mohadjer, Solmaz, and Grey, D.M., in press, Reconnaissance geologic map of the Western Aleutian Islands, Alaska - Integrated geologic map databases of the United States: U.S. Geological Survey Scientific Investigations Map SIM-XXXX, scales 117 Qs Surficial deposits, undivided Quaternary Unconsolidated beach, eolian, delta, lagoon, landslide, glacial, and alluvial deposits composed of silt, sand, gravel, and boulder-sized material. Primary and reworked pyroclastic material is a common component. In many locations, this deposit includesWilson, F.H., Mohadjer, Solmaz, and Grey, D.M., in press, Reconnaissance geologic map of the Western Aleutian Islands, Alaska - Integrated geologic map databases of the United States: U.S. Geological Survey Scientific Investigations Map SIM-XXXX, scales 106 Qf Alluvial fan deposits Quaternary Sand, gravel, and cobbles on Attu Island (Gates and others, 1971). On northern Adak Island, may contain variable amounts of debris-flow deposits and talus, usually mantled by tephra (Waythomas, 1995) 107 Qc Colluvial deposits Quaternary Boulders and boulder-sized debris in slope wash, talus, landslide, and mudflow deposits on Little Sitkin Island (Snyder, 1959). Locally, clasts consist of kaolinized, silicified, and pyritized rock. Includes accumulations of poorly sorted, angular rock 108 Qls Landslide and mudflow deposits Quaternary Poorly sorted accumulations of gravel, sand and silt on Great Sitkin Island (Simons and Mathewson, 1955; Waythomas and others, 2003) and Kanaga Volcano (Miller and others, 2003). Also common on the lower slopes of Mount Moffett and Mount Adagdak and fou 115 Qb Beach deposits Quaternary Sand, pebbles, gravel, and boulders and some narrow stretches of bare rock shore platform. These deposits are distinguished on Adak (Waythomas, 1995), Great Sitkin (Waythomas and others, 2003), Kanaga (Miller and others, 2003), Ogliuga and Skagul (Frase 120 Qd Eolian deposits Quaternary Sand dunes, typically consisting of sand derived from beaches mapped on northern Adak, Kiska, Semisopochnoi, Little Sitkin, Ogliuga, Skagul, and Amchitka Islands (Coats, 1956a; Coats, 1959b; Coats and others, 1961; Snyder, 1959; Fraser and Barnett, 1959; 125 Qg Glacial deposits, undivided Quaternary Ground, terminal, or lateral moraine deposits as well as local outwash. Consists of subangular and rounded boulders, many faceted, in a semi-indurated tough and clayey matrix on northern Adak Island (Coats, 1956a). On southern Adak and Kagalaska Island 295 QhddAnthropogenic deposits Holocene Unconsolidated deposits concentrated around the former Adak Naval Air Station derived from filling low-lying marsh areas and reworking other deposits to construct runways and other facilities. Equivalent to "disturbed land" map unit of Waythomas (1995) 282 QTs Older silt, sand, and gravel Quaternary or Tertiary Boulder-rich conglomeratic deposit on the east flank of Mount Adagdak, mapped as Tertiary by Coats (1956a), is probably Quaternary in age, certainly Pliocene or younger. The cobbles and boulders range in size from a few inches (~5 cm) to 10 feet (3m) an 284 QTs Older silt, sand, and gravel Quaternary or Tertiary Boulder-rich conglomeratic deposit on the east flank of Mount Adagdak, mapped as Tertiary by Coats (1956a), is probably Quaternary in age, certainly Pliocene or younger. The cobbles and boulders range in size from a few inches (~5 cm) to 10 feet (3m) an 290 QTf Faneto Formation early Pleistocene or late Tertiary Pebble, cobble, and boulder conglomerate, coarse sandstone, coarse graywacke, and thin argillite lenses 1,500 feet thick on Attu Island (Gates and others, 1971). Beds are predominantly red (from abundance of pebbles of red argillite or lava) and greenis 475 QTkhKiska Harbor Formation Quaternary(?) and late Tertiary Subaerial lava flows, autoclastic breccias, pyroclastic rocks, water-laid pumiceous sand and conglomerate (Coats and others, 1961) on Kiska and Little Kiska Islands. Flows are predominant in the formation to the north and sedimentary (water-laid) beds t 476 QTkbKiska Harbor Formation, breccia member Quaternary(?) and late Tertiary Volcanic breccia consisting of coarse angular to sub-rounded basalt fragments in a dark-brownish-gray, fine-grained volcanic debris matrix (Coats and others, 1961). The proportion of basalt fragments varies; locally, fragments are uncommon and the brecc 477 QTkfKiska Harbor Formation, flow member Quaternary(?) and late Tertiary Vitrophyric basalt lava flow, lacking pillows and therefore presumably of subaerial origin. Flows in the Kiska Harbor Formation range in thickness from "* * * a few to several hundred feet." (1 to 100 m?) (Coats and others, 1961) 1050Tcp Chitka Point Formation Tertiary, Miocene Subaerial hornblende- and pyroxene-andesite lava flows, breccia, tuff, and marine conglomerate on Amchitka Island (Powers and others, 1960). Thickness exceeds 1000 feet on Amchitka Island as reported by Powers and others (1960). Carr and others (1970) 572 Tch Chuniksak Formation and similar rocks Tertiary, Miocene Fine-grained, well-bedded, laminated siliceous, argillic, and limy marine sedimentary rocks on Attu Island (Gates and others, 1971). According to Gates and others (1971), the formation consists principally of siliceous shale, argillite, calcareous argil 610 Tc Chirikof Formation Tertiary, Miocene? Boulder and pebble conglomerate, coarse sandstone, carbonaceous shale and sandstone, and possibly a single lava flow on Attu Island southwest of Chirikof Point (Gates and others, 1971). The boulder conglomerate contains rounded boulders, whereas fragmen 650 Tn Nevidiskov Formation Tertiary, early Miocene? or late Oligocene?Coarse graywacke and conglomerate in a generally fining upward sequence on Attu Island (Gates and others, 1971). Conglomerate clasts are as much as 2 feet (0.7 m) in diameter, consisting of basement rocks of Attu Island (map unit TMzu), which include po 750 Tgc Gunners Cove Formation Tertiary Tuffaceous conglomerate and sandstone, crystal-vitric basaltic tuff, thin basalt flows, and basaltic dikes (Lewis and others, 1960) forming two-thirds of Rat Island. Sandstone and conglomerate contain moderately to well-rounded mafic volcanic clasts, pr 751 Tbp Banjo Point Formation Tertiary, Oligocene or late Eocene Bedded marine sandstone, conglomerate, tuffaceous shale, and lapilli tuff of basaltic composition on Amchitka Island (Powers and others, 1960). Carr and others (1970) slightly revised the unit definition and the defined outcrop area and also indicated t 800 Tal Andrew Lake Formation and similar rocks Tertiary, late Eocene Tuffaceous sandstone and siltstone and siliceous and cherty shale interbedded with mafic flows or penecontemporaneous sills on Adak and Amatignak Islands. "Graded sandstone beds as much as 0.3-m-thick are common and alternating beds of sandstone and sh 1530Tk Krugoli Formation early Tertiary or late Mesozoic? Bedded argillite, siltstone, chert, basaltic and spilitic lava flows, tuff, tuff-agglomerate, and conglomerate about 7,400-feet-thick on Agattu Island (Gates and others, 1971). Lithologically similar to the basement rocks of Agattu and Attu Islands (map 1540Tkc Krugoli Formation, Coarse-grained and conglomeratic sedimentary rocksearly Tertiary or late Mesozoic? Coarse graywacke and conglomerate, interbedded with pillow lava flows, pyroclastic rocks, and fine siliceous rocks. Clasts consist of sandstone, fine-grained siliceous sedimentary rocks, basalt and tuff; no schistose or granitic clasts were observed (Ga 1094Tkv Krugoli Formation, Tuff and lava; chiefly basaltic and spilitic early Tertiary or late Mesozoic? A single sequence of volcanic rocks about 2,400 feet above base of unit consists of 200 feet of massive green tuff and tuffaceous sandstone overlain by a 50-foot-thick porphyritic basalt flow or by porphyritic basalt pillow lava, in turn overlain by 70 f 1550TMzuBasement rocks, undifferentiated early Tertiary or late Mesozoic? Basement rocks - undifferentiated. On Agattu Island, consist of marine argillite, sandstone, graywacke, and conglomerate, submarine pyroclastic rocks, and columnar-jointed and pillow lava flows (mostly basaltic). Sedimentary rocks are subdivided on Att 1095Tkv Krugoli Formation, Tuff and lava; chiefly basaltic and spilitic early Tertiary or late Mesozoic? A single sequence of volcanic rocks about 2,400 feet above base of unit consists of 200 feet of massive green tuff and tuffaceous sandstone overlain by a 50-foot-thick porphyritic basalt flow or by porphyritic basalt pillow lava, in turn overlain by 70 f 1552TMzfBasement rocks, Fine-grained sedimentary rocks early Tertiary or late Mesozoic? Fine-grained, thin-bedded, sedimentary rocks including chert, siliceous siltstone, argillite, limestone, and fine tuffaceous graywacke in "* * * thin varicolored black, green, red, yellow, and gray beds" (Gates and others, 1971, p. 715), distinguished on 1553TMzcBasement rocks, Coarse-grained and conglomeratic sedimentary rocks early Tertiary or late Mesozoic? Coarse graywacke and conglomerate, interbedded with pillow lavas, pyroclastic rocks, and fine siliceous rocks on Attu Island. Generally drab dark-gray, grayish-purple, or grayish-green in thin beds of graywacke and much thicker conglomerate horizons. T 1096Tbv Basement rocks, Volcanic rocks Tertiary? Largely tuff and tuff-agglomerate of generally basaltic composition and interbedded pillow lava flows on Attu and Agattu Islands. Pyroclastic rocks range from coarse, bomb-filled lapilli tuff to fine-grained, silt-sized tuff, agglomerate, and breccia. 300 Qvu Volcanic rocks and deposits, undivided Quaternary Consists of basalt and andesite lava flows, minor intrusive rocks, and pyroclastic rocks and deposits, including scoria, tuff breccia, and vent agglomerate throughout the western Aleutian Islands. These include the rocks and deposits of the older stag 355 Qvu Volcanic rocks and deposits, undivided Quaternary Consists of basalt and andesite lava flows, minor intrusive rocks, and pyroclastic rocks and deposits, including scoria, tuff breccia, and vent agglomerate throughout the western Aleutian Islands. These include the rocks and deposits of the older stag 402 Qvu Volcanic rocks and deposits, undivided Quaternary Consists of basalt and andesite lava flows, minor intrusive rocks, and pyroclastic rocks and deposits, including scoria, tuff breccia, and vent agglomerate throughout the western Aleutian Islands. These include the rocks and deposits of the older stag 404 Qvu Volcanic rocks and deposits, undivided Quaternary Consists of basalt and andesite lava flows, minor intrusive rocks, and pyroclastic rocks and deposits, including scoria, tuff breccia, and vent agglomerate throughout the western Aleutian Islands. These include the rocks and deposits of the older stag 305 Hv Younger volcanic rocks Holocene Largely consists of basalt flows and interbedded pyroclastic rocks associated with Moffett Volcano and Mt. Adagdak on Adak Island (Coats, 1956a), on Kiska Volcano on Kiska Island (Coats and others, 1961), and Mount Cerberus, Sugarloaf Peak, and Lakeshore 310 Hp Pyroclastic rocks Holocene or late Pleistocene? Includes pyroclastic rocks and deposits of dacitic and andesitic composition and minor lava flows associated with Great Sitkin Volcano on Great Sitkin Island (Qat, Simons and Mathewson, 1955; Qat, Qhts, Qpf, Waythomas and others, 2003), the older composi 311 Ha Ash and tephra deposits Holocene Constructional surfaces on Segula and possibly Davidof and Khvostof (Nelson, 1959), and on northern Adak Island (Waythomas, 1995) are covered by a pyroclastic mantle. On Segula Island, it consists of clasts ranging in size from fine sand to large blocks 336 Hd Little Sitkin Dacite and Double Point Dacite Holocene and late Pleistocene? White to black low-silica dacite and rhyodacite flows of the Little Sitkin Dacite locally subdivided into the West Cove and Pratt Point members (Snyder, 1959) and a sequence of light- to dark-gray high-silica dacite flows containing many miarolitic inclu 306 Hvd Basalt and andesite domes Holocene In part consists of dark-gray to black, glassy, porphyritic basalt dome extruded in crater of Great Sitkin Volcano in 1945, largely removed by 1974 eruption (Unit Qld45, Waythomas and others, 2003). Also includes a dark-gray to black, basaltic andesite 313 Ql Lahar and debris avalanche deposits Quaternary Poorly sorted gravel, sand, silt, and boulders in fan-shaped deposits on Great Sitkin and Kanaga Volcanoes (Waythomas and others, 2003; Miller and others, 2003). These deposits are present in most major valleys ranging from 1 to 5 meters in thickness. 314 Ql Lahar and debris avalanche deposits Quaternary Poorly sorted gravel, sand, silt, and boulders in fan-shaped deposits on Great Sitkin and Kanaga Volcanoes (Waythomas and others, 2003; Miller and others, 2003). These deposits are present in most major valleys ranging from 1 to 5 meters in thickness. 320 Qvv Vent volcanic rocks and deposits Holocene and late Pleistocene Dark-gray, glassy or fine-grained, compact or diktytaxitic, porphyritic feldspathic basalt associated with the central and rift vents of Segula Volcano (Nelson, 1959) as well as the tuff-breccia cone of Mount Moffett Volcano on Adak Island (Coats, 1956a) 330 Qvv Vent volcanic rocks and deposits Holocene and late Pleistocene Dark-gray, glassy or fine-grained, compact or diktytaxitic, porphyritic feldspathic basalt associated with the central and rift vents of Segula Volcano (Nelson, 1959) as well as the tuff-breccia cone of Mount Moffett Volcano on Adak Island (Coats, 1956a) 335 Qep East Point Formation Quaternary Andesite and basalt flows more than 500-feet-thick exposed at East Point on Little Sitkin Island (Snyder, 1959). Flows tend to be massive with clinkery, vesicular flow tops. These flows were erupted onto a deeply dissected topography and this relations 317 Qsp Sitkin Point Formation and similar rocks Quaternary Water laid pyroclastic material including tuffaceous graywacke, dacite-boulder tuff-breccia, andesitic tuff, and pumiceous tuff on Little Sitkin Island (Snyder, 1959). Locally includes areas of kaolinized, silicified, and pyritized rock. Also includes 450 QTv Older volcanic rocks, undivided Quaternary and Tertiary Includes the Pochnoi Volcanics of Semisopochnoi Island (Coats, 1959b) consisting of tuff-breccia, lava flows, and agglomerate, as well as largely basaltic and olivine and hypersthene basalt and andesite flows of ancestral Mt. Kanaton volcano on Kanaga Is 451 QTv Older volcanic rocks, undivided Quaternary and Tertiary Includes the Pochnoi Volcanics of Semisopochnoi Island (Coats, 1959b) consisting of tuff-breccia, lava flows, and agglomerate, as well as largely basaltic and olivine and hypersthene basalt and andesite flows of ancestral Mt. Kanaton volcano on Kanaga Is 460 QTv Older volcanic rocks, undivided Quaternary and Tertiary Includes the Pochnoi Volcanics of Semisopochnoi Island (Coats, 1959b) consisting of tuff-breccia, lava flows, and agglomerate, as well as largely basaltic and olivine and hypersthene basalt and andesite flows of ancestral Mt. Kanaton volcano on Kanaga Is 466 QTv Older volcanic rocks, undivided Quaternary and Tertiary Includes the Pochnoi Volcanics of Semisopochnoi Island (Coats, 1959b) consisting of tuff-breccia, lava flows, and agglomerate, as well as largely basaltic and olivine and hypersthene basalt and andesite flows of ancestral Mt. Kanaton volcano on Kanaga Is 470 QTv Older volcanic rocks, undivided Quaternary and Tertiary Includes the Pochnoi Volcanics of Semisopochnoi Island (Coats, 1959b) consisting of tuff-breccia, lava flows, and agglomerate, as well as largely basaltic and olivine and hypersthene basalt and andesite flows of ancestral Mt. Kanaton volcano on Kanaga Is 350 QTb Basalt plugs and associated breccia Quaternary or Tertiary Includes basalt plugs of the Great Sitkin Volcanics (Simons and Mathewson, 1955), basalt flows and tuff-breccia from a vent older than caldera of Mt. Kanaton near west coast of Kanaga Island (Coats, 1956b). Also includes porphyritic fine-grained, column 454 QTobOlivine basalt flows Quaternary or Tertiary Olivine basalt flows from vent older than caldera of Mt. Kanaton near Round Head on northern Kanaga Island (Coats, 1956b; Miller and others, 2003). A K-Ar whole-rock age determination yielded an zero age for basaltic andesite (Bingham and Stone, 1972), 462 QTqkQuartz keratophyre dikes Early Quaternary or Late Tertiary Quartz keratophyre dikes (Gates and others, 1971) on widely separated parts of Attu Island. Dikes consist of chalky white euhedral feldspar (albite) crystals and glassy quartz in a bluish-gray to light-gray groundmass of fine-grained albite, quartz and 463 QThaHornblende andesite and dacite Early Quaternary or Late Tertiary Porphyritic dikes and stocks of hornblende andesite and dacite on Attu Island (Gates and others, 1971). A hornblende dacite porphyry from this unit that cuts the Chirikof Formation, map unit Tc, yielded a 6.1 ñ 0.4 Ma whole-rock K-Ar age (DeLong and McD 1066Tlp Lavas and pyroclastic deposits, undifferentiated Miocene or older Basaltic or andesitic lava and pyroclastic deposits on Kavalga, Ogliuga, Ulak, and Skagul Islands (Fraser and Barnett, 1959). Locally subdivided into predominantly lava and flow breccia, and tuff and breccia units, in some places fractured and silicifie 1080Tvb Vega Bay Formation middle Tertiary Marine deposits of volcanic breccia, tuff, and a few pillow lava flows, all of basaltic composition, with a few interbeds of conglomerate and sandstone of similar material on Kiska Island (Coats and others, 1961). Samples from flows, a dike, and a basal 1081Tvo Finger Bay Volcanics and similar rocks Tertiary, Oligocene or older Herein consists of the Finger Bay Volcanics of Adak and Kagalaska Islands and most of the Andreanof Islands east of Adak Island (Coats, 1956a; 1956c; Fraser and Snyder, 1959), the Amchitka Formation of Amchitka Island (Powers and others, 1960; Carr and o 1010Tid Dikes and hypabyssal intrusive rocks Tertiary Dikes and small intrusive bodies largely of basalt and andesite, but includes altered basalt in small dikes and sills on southern Adak and Kagalaska Islands (Coats, 1956a; Fraser and Snyder, 1959). According to Fraser and Snyder (1959), dikes in the Fin 1011Tid Dikes and hypabyssal intrusive rocks Tertiary Dikes and small intrusive bodies largely of basalt and andesite, but includes altered basalt in small dikes and sills on southern Adak and Kagalaska Islands (Coats, 1956a; Fraser and Snyder, 1959). According to Fraser and Snyder (1959), dikes in the Fin 1012Tid Dikes and hypabyssal intrusive rocks Tertiary Dikes and small intrusive bodies largely of basalt and andesite, but includes altered basalt in small dikes and sills on southern Adak and Kagalaska Islands (Coats, 1956a; Fraser and Snyder, 1959). According to Fraser and Snyder (1959), dikes in the Fin 1051Tid Dikes and hypabyssal intrusive rocks Tertiary Dikes and small intrusive bodies largely of basalt and andesite, but includes altered basalt in small dikes and sills on southern Adak and Kagalaska Islands (Coats, 1956a; Fraser and Snyder, 1959). According to Fraser and Snyder (1959), dikes in the Fin 1207Td Diabase and gabbro Tertiary Diabase and gabbro dikes, sills and small plutons are widespread and form two-thirds of the intrusive rocks on Attu Island as well as being very common on Agattu Island (Gates and others, 1971). These dikes and sills intrude all Attu Island units as old 1250TqgdQuartz diorite and granodiorite Tertiary, Miocene Younger granodiorite, quartz diorite, and gabbro in stocks, sills, and dikes on Adak and Kagalaska Islands (Fraser and Snyder, 1959) and quartz diorite on Amchitka Island (Powers and others, 1960). On Amchitka Island, medium-grained quartz diorite intru 1203TagrAlbite granite Tertiary Albite granite is found on Attu Island in the Steller Cove and Mikhail Point areas (Gates and others, 1971). It occurs in irregular masses at Steller Cove and as a small stock east of Mikhail Point. The granite is gray, pale-pink, or purplish, has wide 1292Tgd Granodiorite, quartz diorite, and gabbro Tertiary Older granodiorite, quartz diorite, and gabbro in stocks, sills, and dikes on Adak Island; originally mapped as the same unit as our Tqgd by Fraser and Snyder (1959, their unit gd), K-Ar dating has shown that these plutons are of 2 separate ages (Marlow