Qs
Surficial deposits, undiivided
Quaternary
Unconsolidated, poorly to well-sorted, poorly to moderately well-stratified deposits; consists predominantly of alluvial, colluvial, glacial, marine, lacustrine, eolian, and swamp deposits
Wilson, F.H., in prep., Reconnaissance geologic map for the Kodiak Islands, Alaska - Integrated geologic map databases of the United States:  U.S. Geological survey Scientific Investigations Map SIM-XXXX, scale 1:500,000.
Qa
Alluvial deposits
Range from coarse, sub-angular rock fragments to fine sand and silt; locally includes considerable amounts of pumice near volcanic centers
Wilson, F.H., Detterman, R.L., and DuBois, G.D., in press, Geologic framework of the Alaska Peninsula:  U.S. Geological Survey Bulletin 1969-B, pamphlet, scale 1:500,000.
Qaf
Alluvial fan deposits
Range from coarse, sub-angular rock fragments to fine sand and silt.  Typically have well-developed cone shapes or are multiple cones coalescing into aprons
Qls
Landslide deposits
Coarse, sub-angular rock fragments to fine sand and silt having poorly to well-developed lobate morphology
Qb
Marine beach and estuarine deposits
Marine beach and estuarine deposits.  Moderately well-stratified and sorted sand and gravel on beaches; mud and silt in estuaries
Qmt
Marine terrace deposits
Marine terrace deposits.  Stratified and moderately well sorted sand and gravel deposits that form nearly level plains ending locally at prominent wave-cut scarps.  Terraces occur between 40 and 45 m elevation along Pacific Ocean on the Alaska Peninsula
Qrg
Rock glacier deposits
Holocene
Consist of poorly sorted rock fragments and debris in lobate forms and typically ice-cored (Detterman and others (1987b)
Qad
Drift, Alaskan Glaciation (Neoglacial)
Consists of undivided glacial deposits at the outer limits of modern glaciers, glacier remnants, and in isolated cirques (Detterman and others (1987b)
Qblu
Drift, undivided, Brooks Lake Glaciation
Pleistocene
Consists of undivided glacial deposits including end, lateral, recessional, and ground moraine and outwash (Detterman and others (1987b)
Qbln
Drift, Newhalen advance, Brooks Lake Glaciation
Consists typically of end and lateral moraine of the Newhalen advance, the second youngest of the four advance Brooks Lake Glaciation of generally accepted late Wisconsin age (Detterman and others (1987b)
Qblil
Drift, Iliamna advance, Brooks Lake Glaciation
Consists typically of end and lateral moraines of the second oldest of the four advance Brooks Lake Glaciation.  This advance was significantly more extensive than younger advances and tends to have well-developed morainal features.  Is generally accepte
Qmhd
Drift, Mak Hill Glaciation
Consists of undivided glacial deposits including end, lateral, recessional, and ground moraine and outwash (Detterman and others, 1987b).  Older than late Wisconsin age
Qv
Volcanic rocks, undivided
Andesite, dacite, and leucobasalt lava flows, volcanic breccia, lahar deposits, and debris-flow deposits.  Includes air-fall tuff, volcanic dome deposits, block-and-ash-flow deposits, ash-flow tuffs, volcanic-rubble flows, debris flows and hot-blast aval
QTv
Volcanic rocks
Quaternary and Pliocene?
Andesite and basalt lava flows, sills, and plugs.  These primarily extrusive rocks typically cap ridges and include massive lava flows, agglomerate, and lahar deposits
Tsu
Sedimentary rocks, undivided
Tertiary
Includes a number of different units mapped in various areas throughout the map area:
  In the Healy quadrangle, unit Ts (Csejtey and others, 1992) consists of a sequence of poorly consolidated fluviatile dark-gray shale, yellowish-gray sandstone, siltst
Wilson and others, 1998 (DOGmap)
Ttg
Tugidak Formation
late Pliocene and early Pleistocene
Consists of 1,500 m of interbedded sandstone and siltstone characterized by randomly distributed pebbles and cobbles.  Includes randomly distributed pebbles and cobbles of glacial-marine origin (Allison, 1978).  A single 1-m-thick cobble conglomerate bed
Ty
Albatross sedimentary sequence of Clendenen and others (1992)
Pliocene or late Miocene
Diamictite, sandstone, and siltstone.  Conglomerate horizons contain clasts of granite, chert, melange, and slate.  Also contains distinctive calcareous shale clasts unlike any nearby exposed units.  Calcareous shale clasts contain a late early Miocene f
Tnc
Narrow Cape Formation
middle Miocene
Unit is 700-m-thick, the lower 2/3 consisting of sandstone and a few conglomerate beds.  The upper third is siltstone.  A basal sedimentary breccia and conglomerate contains clasts derived from the underlying Sitkalidak Formation; this unit is fossilifer
Tsti
Siltstone of Trinity Islands of Clendenen and others (1992)
earliest Miocene or late Oligocene
Siltstone deposited in cool-temperature climactic conditions at outer neritic water depths.  Originally included in the Narrow Cape Formation, is now considered a distinctive, older unit.  It is highly bioturbated siltstone and very fine-grained sandston
Tcb
Fresh-water sandstone, shale, and conglomerate, locally containing coly seams
Fresh-water sandstone, shale, and conglomerate, locally containing coly seams.  Generally steeply dipping and well indurated; locally highly contorted.  (Includes Sitkinak and Sitkalidak Formations).  Unit not used on this map.
Capps, S.R., 1937, Kodiak and adjacent islands, Alaska:  U.S. Geological Survey Bulletin 880-C, p. 111-184.
Th
Hemlock Conglomerate
late Oligocene
Composed primarily of fluvial sandstone and conglomerate that contains interbeds of siltstone, shale, and coal.  Chert, quartz, and granitic and metasedimentary rocks form most of clasts in conglomerate; volcanic rocks are small, but significant, proport
Tsk
Sitkinak Formation
Oligocene
Conglomerate and cross-bedded sandstone and siltstone containing coal fragments.  Unit is 1,500-m-thick in its type section along the south shore of Sitkinak Island.  According to Nilsen and Moore (1981), the outcrops of the Sitkinak Formation consist of
Tsi
Sitkalidak Formation
Oligocene and Eocene
Uniform sandstone and siltstone in graded beds and a few conglomerate beds for a total thickness of about 3,000 m.  A fossil crab, Callianassa aff. C. porterensis, indicates an Oligocene age (Moore, 1969); Moore (1969) assigned an Eocene and Oligocene ag
Tc
Copper Lake Formation
early Eocene and Paleocene(?)
Consists of thick pebble-cobble conglomerate in its uppermost and lowermost parts and contains sandstone and siltstone in its middle part.  In measured section, conglomerate intervals are massive and have clasts that are a mixture of volcanic, granitic,
Tghc
Ghost Rocks Formation, coherent sedimentary rocks
Paleocene and Late Cretaceous?
Unit B of Byrne (1981), these rocks are exposed in the vicinity of Jap Bay.  They consist "* * * of medium-bedded (10-40 cm thick beds) sandstone interbedded with similar thicknesses of shale.  The sandstones and shales are rhythmically bedded and sole m
Tghs
Ghost Rocks Formation, sandstone-rich unit, undivided
Paleocene?
Massive sandstone beds and lesser amounts of argillite and medium- to thin-bedded sandstone.  Sandstone beds show Bouma sequences indicative of deposition be turbidity currents.  Locally, channelized conglomerate units up to 100-m-thick occur on the Aliu
Tgha
Ghost Rocks Formation, argillite-rich unit, undivided
Thick sections of argillite and local massive sandstone and chert-rich pebble conglomerate.  Locally contains tuff beds.  Limestone containing planktic foraminifers occurs locally at depositional contacts with pillow basalt.  Unit typically occurs to sou
Tab
Volcanic rocks of Barrier Range
late Tertiary
Breccia, lava flows, sills, and local pyroclastic and epiclastic tuff, southeast of active part of Aleutian Arc
Tgvb
Ghost Rocks, basaltic volcanic and hypabyssal rocks
Tertiary or Cretaceous?
Tholeiitic basalt occurring within both sandstone- and argillite-rich subunits of the Ghost Rocks Formation.  Rocks are typically altered by shearing and low-grade metamorphism, yet "* * * these lavas cannot have been derived from a single source and in
Ti
Intrusive rocks
Pliocene and late Miocene
Medium- to coarse-grained, equigranular, granodiorite to quartz diorite plutons and stocks.  Typically surrounded by well-developed hornfels zones and sporadic hydrothermal alteration in country rocks.  Intrusive bodies typically located along Pacific co
Tegr
Younger granitic rocks
Eocene?
Small altered granitic plutons intrude the Ghost Rocks Formation between Portage and Kaingnak Bays and north of Ugak Bay on the southeast coast of Kodiak Island.  Examination of a few thin-sections of these plutons show them to be distinctive from the Ko
Tg
Granitic rocks
Paleocene
Generally consists of fine-grained biotite quartz monzonite of the Kodiak batholith.   Range in composition from two-mica granite to granodiorite.  Intrude flysch deposits of the Kodiak Formation and in the vicinity of Jap Bay, intrude the Ghost Rocks Fo
Tgh
Ghost Rocks Formation, undivided
Consists of zeolite-bearing tuffaceous sandstone and basalt, and hard claystone, sandstone, tuff, and graded beds (wildflysch of Moore, 1969).  The formation is sheared, faulted, and folded; the estimated thickness is 5,000 meters (Nilsen and Moore, 1981
Kkd
Kodiak Formation
Late Cretaceous
Consists of medium- to thick-bedded graded bed sequences, averaging 1-m-thick, of arkosic wacke and shale having occasional beds of pebbly conglomerate.  Flute casts and complete Bouma sequences indicate deposition by turbidity currents below wave base.
Kk
Kaguyak Formation
Consists of a measured thickness of more than 1,200 m of dark-gray to pale-brown, typically thin-bedded, shale, siltstone, and fine-grained sandstone.  Proportion of sandstone in unit increases up-section.  Load and flute casts are common; in upper part
Kcct
Cape Current terrane of Connelly (1978)
An informal unit described by Connelly (1978) as consisting principally of medium- to thick-bedded arkosic and lithic sandstone containing occasional sections of vesicular pillow lava and pillow breccia.  Slightly metamorphosed and moderately deformed.
Khe
Herendeen Formation
Early Cretaceous
Originally described as limestone, rocks of formation are actually an unusually uniform calc-arenaceous sandstone.  Rocks are thin-bedded, medium-grained, and dusky yellow to pale-yellowish-brown on freshly broken surfaces and weather to conspicuous ligh
Kmk
Uyak Complex
"Lithologically chaotic assemblage of deep-sea rock types." (Connelly and Moore, 1979)  Includes:  argillite and gray chert containing minor tuff; massive arkosic sandstone; pillowed and massive greenstone; bedded radiolarian chert; minor limestone; and
Kmu
Gabbroic and ultramafic rock
Unknown age, assigned to melange
Gabbroic and ultramafic rock, including layered gabbro, clino-pyroxenite, dunite, and plagioclase peridotite.  Occur as kilometer-sized slabs in the northwesternmost exposures of the Uyak that are always fault-bounded (Connelly, 1978).  The margins of th
Jn
Naknek Formation
Late Jurassic
Thin- to thick-bedded, intercalated fossiliferous gray siltstone, shale, sandstone, and conglomerate more than 1,400-m-thick (Csejtey and others, 1978).  Originally named Naknek Series by Spurr (1900, p. 169-171, 179, 181) for exposures at Naknek Lake on
Jnn
Naknek Formation, Northeast Creek Sandstone Member
Oxfordian
Type section consists of 624 m of fine- to coarse-grained, light-brownish-gray arkosic sandstone and minor amounts of olive-gray to dark-gray, thin-bedded siltstone in lower part of section (Detterman and others, 1996).  Sandstone is typically thick-bedd
Jnst
Naknek Formation, Snug Harbor Siltstone Member
Kimmeridgian and Oxfordian
Reference section consists of more than 638 m of dark-yellowish-brown and dark-gray, thin-bedded siltstone and minor amounts of thin- to medium-bedded olive-gray sandstone (Detterman and others, 1996).  Limestone nodules are locally abundant, and limesto
Jni
Naknek Formation, Indecision Creek Sandstone Member
Tithonian and Kimmeridgian
Consists of medium-gray, fine- to medium-grained arkosic sandstone and siltstone (Detterman and others, 1996).  It is thin-bedded to massive; where bedded, it is locally crossbedded.  Fresh biotite and hornblende are minor, but important, components of s
Jnc
Naknek Formation, Chisik Conglomerate Member
Limited to northern half of Alaska Peninsula, consists of massive to thick-bedded conglomerate and interbedded, crossbedded, clean quartzose sandstone.  Clasts as large as 2 m.  Clast composition is mainly granitic rocks, and up to 20 percent metamorphic
Js
Shelikof Formation
Middle Jurassic
Massive to thick-bedded, medium- to coarse-grained, dark-green to gray volcanogenic sandstone containing abundant magnetite grains (Detterman and others, 1996).  Interpreted to have been deposited in a deep- to shallowing water environment (Detterman and
Jk
Kialagvik Formation
Middle and Early Jurassic
Olive-gray to green, medium-bedded, fine- to medium-grained graywacke, mudstone, siltstone, and shale; local lenses of volcanic pebble conglomerate (Detterman and others, 1996).  Shallow-water deposits of Kialagvik Formation are abundantly fossiliferous;
Jt
Talkeetna Formation
Early Jurassic, Late Triassic?
Lower part composed of dark-gray tuffaceous limestone, tuff, and dark siliceous shale.  Upper part thin to massive tuffaceous gray sandstone with minor siltstone and shale interbeds (Detterman and others, 1996).  Age of unit, Early Jurassic (Hettangian a
Wilson and others, 1998 (apmap)
Jsch
Schist of Kodiak Island
Jurassic
Thinly layered and complexly folded quartz-mica schist, greenschist, crossite-epidote schist (blueschist), and epidote amphibolite (Connelly and Moore, 1979).  Subdivided into two units by Roeske and others (1989, called the Raspberry Schist), the first
Trk
Kamishak Formation
Late Triassic
Detterman and Reed (1980) divided unit into three members, in ascending order, Bruin Limestone Member, middle member, and Ursus Member.  On Alaska Peninsula, Triassic limestone strata were assigned to the Bruin(?) Limestone Member of the Kamishak Formati
Trss
Shuyak Formation, sedimentary member
Consists of two members, a sedimentary unit in fault contact with a volcanic member, which it is inferred to overlie (Connelly and Moore, 1979).  The unit structurally overlies the schist of Kodiak Island (Jsch) and Uyak Complex (Kmk), but is generally s
Trv
Columnar-jointed basalt flows, volcanic breccia, and agglomerate.  Chemical data (Hill, 1979; Wilson and Shew, 1992) indicate these rocks are of tholeiitic affinity.  Interbedded with Late Triassic Kamishak Formation (Trk).  Potassium-argon age determina
Trvm
Mafic dikes, sills, and plugs
Triassic?
Diabasic bodies intruding Shuyak Formation having no apparent thermal aureoles (Connelly and Moore, 1979)
Trsv
Shuyak Formation, volcanicmember
Trqd
Afognak pluton
Triassic
Large, multiphase hornblende diorite, quartz diorite, and tonalite pluton exposed along the northwest side of the Kodiak Islands (Connelly and Moore, 1979; Roeske and others, 1989).  The pluton has a well-developed contact metamorphic aureole with the Sh
Pls
Limestone
Permian
Consists  of 40 m of thin- to thick-bedded, medium-grained, crystalline tan to gray limestone containing thin interbeds of chert, located on a small islet (100 by 200 m) at entrance to Puale Bay.  No contacts are exposed, although highly contorted beds d
Pv
Permian(?)
Massive, dark-green to black volcanic breccia, agglomerate, and andesitic flows (Hanson, 1957; Hill, 1979).  These rocks are only exposed on offshore islets east of Puale Bay.  Well-developed joint system has obscured original structure, and because of t