Qs?
Surficial deposits
Quaternary
Undivided surficial deposits
KD002
Kodiak
Unconsolidated
Qs
Consist of glacial and stream deposits inland and beach sediments along coast
KD004
KR005
Karluk
TI002
Trinity Islands
KG002
Kaguyak
Holocene and Pleistocene
Unconsolidated, porrly to well-sorted, poorly to moderately well-stratified doeposits; consists predominatly of alluvial, colluvial, glacial, marine, lacustrine, eolian, and swamp deposits.  Also, locally includes reworked volcanic debris as well as bloc
KR002
Surficial deposits, undivided
AF002
Afognak
Alluvium and marine terrace deposits
TI004
KR006
Consists of glacial and stream deposits inland and beach sediments along coast
AF004
Qmg
Present stream gravel, sand, and silt
Quaternary, Pleistocene and Recent
Low terrace gravel; alluvial fans; beach deposits.  Glacial morainal material
AF010
KD007
KR009
KG007
AF005
Qa
Alluvial deposits
Ranges from coarse, subangular rock fragments to fine sand and silt in grainsize; locally includes considerable amounts of pumice near volcanic centers.
AF006
Qaf
Alluvial fan and landslide deposits
Locally mapped; grainsize in this unit ranges from coarse, subangular rock fragments to fine sand and silt.  Alluvial fans either typically have a well-developed cone shape, or multiple cones coalescing into aprons.  Landslide deposits have poorly develo
Qls
Landslide deposits
Lanslide deposits
KR003
Landslide deposits ranging from nonsorted, nonstratifed, coarse angular rubble forming lobes, to large discrete blocks that resemble undisturbed bedrock
ls
Landslide deposits ranging from nonsorted, nonstratifed, coarse angular rubble forming lobste masses at base of moderately steep to steep slopes.  Where derived from bedrock, deposits are chiefly coarse angular blocks; where derived from glacial deposits
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
be
Marine beach deposits
Moderately well stratified and sorted sand and gravel on beaches
Qmt
Marine terrace deposits
Marine terrace deposits.  Stratified and moderately well sorted sand and gravel deposits that form nearly level plains that end locally at prominent wave-cut scarps.  Terraces occur at 15 to 18 m elevation along Bristol Bay and between 40 and 45 m elevat
mt
rg
Rock glacier deposits
Qad
Drift, Alaskan glaciation (Neoglacial)
Holocene
nd
Drift, Neoglacial
Qblu
Drift, undivided, Brooks Lake glaciation
Quaternary, Pleistocene
blu
Qbln
Drift, Newhalen Stade, Brooks Lake Glaciation
Qblil
Drift, Iliamna Stade, Brooks Lake Glaciation
Qmhd
Drift, Mak Hill Glaciation
Qvi
Volcanic and shallow intrusive rocks
Basalitc andesite to dacite lava flows, volcaniclastic deposits.  Includes air-fall tuffs, volcanic domes, block and ash-flow deposits, ash-flow tuffs, volcanic-rubble flows, debris flows and hot-blast avalanche deposits
Igneous
Qv
Volcanic rocks
Andesite, dacite, and leucobasalt lava flows, volcanic breccia, lahar deposits, and debris-flow deposits.  Lava flows and clasts in other volcanic deposits of unit are porphyritic, typically glassy, gray to black, and commonly vesicular.  Andesite is ove
KR004
Qap
Ash-flow and ash-fall deposits
Nonsorted, variably indurated deposits of ash, vitrophyre blocks, and (or) pumiceous lapilli.  Mapped in Valley of Ten Thousand Smokes and  at Kaguyak Crater
Domes
Dacitic or rhyolitic vitrophyres having plagioclase, pyroxene, and (or) hornblende phenocrysts in a brown to grayish-brown glassy groundmass.
cvd
Dacite at Snowy Mountain, Mount Cerberus,  Falling Mountain, and at Kaguyak Crater and rhyolite at Novarupta
QTv
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.
Ttg
Tugidak Formation
Tertiary, Pliocene
Consists of 1,500 m of of interbedded sandstone and siltstone characterized by randomly distributed pebbles and cobbles.  A single 1 m thick cobble conglomerate bed reported 350 m above base of unit
Richly fossiliferous, marine fossils of Pliocene age.
TI003
Sedimentary
Tp
Pliocene marine sedimentary rocks
Mainly Tertiary sandstone and shale
Tertiary
TI006
Albatross sedimentary sequence
Tertiary, Pliocene or late Miocene
Diamictite, sandstone, and siltstone.  Conglomerate horizons contain clasts of granite, chert, melange, and slate.  Also contain distinctive calcareous shale clasts unlike any nearby exposed units
Calcareous shale clasts contain a late early Miocene fauna; enclosing unit is correlate with the Yakataga Formation
Tnc
Narrow Cape Formation
Tertiary, Miocene
Formation is 700m thick, the lower 2/3 consisting of sandstone and a few conglomerate beds.  The upper third consists of siltstone.
KD003
Tms
Miocene sedimentary rocks
Tertiary, Late Miocene
KD006
Marine sandstones of Narrow Point
Marine sandstones of Narrow Point, mildly folded and moderately indurated
Siltstone of Trinity Islands
Tertiary, earliest Miocene or late Oligocene
Siltstone deposited in cool-temperature climactic conditions at outer neritic water depths.  Originally included is the Narrow Cape Formation, is now considered a distinctive, older unit.
Molluscan fauna and benthic foraminifers
Tts
Siltstone of Trinity Island and Sitkinak Formation
Tertiary, Oligocene and Early Miocene
Th
Hemlock Conglomerate
late Oligocene
Composed primarily of fluvial sandstone and conglomerate that contain 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 proportion
Megaflora fossils of broadleaf deciduous plants and evergreen needles suggest late Oligocene age (J.A. Wolfe, written commun., 1988, in Detterman and others, 1996)
Tsk
Sitkinak Formation
Tertiary, Oligocene
Conglomerate and cross-bedded sandstone and siltstone containing coal fragments.
To
Oligocene continental sedimentary rocks
KG003
Conglomerate and sandstone alternating with fine-grained sandstone, siltstone, coal, and carbonaceous shale.  Primarily of terrestrial origin; deposited as channelized braided stream gravels interebedded with interchannel, lagoonal, and interdistributary
Tss
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)
Tsi
Sitkalidak Formation
Tertiary, Oligocene to Eocene
Uniform sandstone and siltstone graded beds about 3,000 m thick  Rare conglomerate beds.
Teo
Eo-Oligocene marine sedimentary rocks
Sitkalidak Formation, slope-basin deposits
Tertiary, Eocene
Less deformed interbedded sandstone and siltstone, mudstone and conglomerate, representative of deep-sea fan deposition.
Sitkalidak Formation, offscraped deposits
More deformed interbedded sandstone and siltstone, mudstone and conglomerate, representative of deep-sea fan deposition.
KG004
Ts
Sitkalidak Formation, undivided
Tertiary, Eocene to Early Oligocene
Tsl
Sitkalidak Formation, less deformed
Tsm
Sitkalidak Formation, more deformed
TI005
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 mixture of volcanic, granitic, an
Age of Copper Lake is not well constrained; sparse megaflora in type section in Iliamna area and abundant megaflora in map area are restricted to sandstone and siltstone intervals that are present in middle part of unit (Detterman and others, 1996).
Tgc
Ghost Rocks Formation, coherent
Tertiary, early Paleocene
KG006
Tgs
Ghost Rocks Formation, sandstone-rich unit, undivided
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
Consists of thick sections of argillite and local massive sandstone and chert-rich pebble conglomerate.  Tuff beds.  Limestone containing pelagic forams locally occurs at depositional contacts with pillow basalt.  Unit typically occurs to southeast of sa
Pelagic forams yielding early Tertiary and Late Cretaceous ages (3 collections)
Tga
Ghost Rocks Formation, argillite-rich unit, undivided
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
Tgva
Ghost Rocks Formation, andesitic volcanic and hypabyssal rocks
Tgvb
Ghost Rocks Formation, basaltic volcanic and hypabyssal rocks
Tholeiitic basalt occurring within both sandstone- and argillite-rich units of the Formation.  Rocks are typically altered by shearing and low-grade metamorphism, yet "* * * these lavas cannot have been derived from a single source and in many respect ex
TKg
Granular intrusive rocks
Latest Cretaceous or Early Tertiary
Granular intrusive rocks, mainly quartz diorite, with some diorite, and minor amounts of gabbro
Q
Tqd
Quartz diorite
Pliocene and (or) Miocene
Fine- to medium-grained, equigranular, quartz diorite, quartz monzodiorite, granodiorite and quartz monzonite.  Intrusive bodies are typically located along Pacific coast and include, but are not limited to, large plutons at Agripina Bay, Mount Becharof,
Potassium-argon ages range from 2.3 to 3.2 Ma (Wilson and  others, 1981; F.H. Wilson and Nora Shew, unpub. data, 1990; Wilson and Shew, 1992)
Ti
Intrusive rocks
Pliocene and late Miocene
Medium- to coarse-grained, equigranular, granodiorite to quartz diorite plutons and stocks containing hornblende, biotite, and pyroxene as mafic minerals and typically are surrounded by well-developed hornfels zones and sporadic hydrothermal alteration i
Potassium-argon ages range from 9.43 +/- 0.26 to 3.21 +/- 0.14 Ma (Wilson and  others, 1981; F.H. Wilson and Nora Shew, unpub. data, 1990; Wilson and Shew, 1992)
Granitic plutonic rocks
Tertiary, Eocene or younger
Small altered granitic plutons that 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 t
KD005
Tqm
Biotite quartz monzonite
Tertiary, Paleocene?
Kodiak batholith
Mobil Oil dates of approximately 62 Ma cited in Byrne (1981, Ph.D.)
Tgd
Granodiorite
Tertiary, Paleocene
Tg
Granitic rocks
early Tertiary
Inferred granitic rocks based on aeromagnetic evidence and unconfirmed reports.
Tgh
Ghost Rocks Formation
Tertiary, Paleocene to Eocene
Consists of zeolite-bearing tuffaceous sandstone, basalt, claystone, sandstone, tuff, and graded beds (wildflysch)
Tectonite
Tpe
Paleocene volcanic and sedimentary rocks
Tgm
Ghost Rocks Formation, melange
Kk
Kodiak Formation
Late Cretaceous
Consists of graded bed sequences an average 1-m-thick of thick medium-grained sandstone grading to thin slate
Inoceramus of Late Cretaceous age
Kkd
Consists of average 1 m thick graded bed sequences of thick medium-grained sandstone grading to thin slate
Late Cretaceous, Maestrichtian
Medium- to thickly bedded arkosic wacke and shale having occaisional beds of pebbly conglomerate.  Flute casts and complete Bouma sequences indicate deposition by turbidity currents below wave base.  Strike NE and dips steeply NW, generally deformed in t
Inoceramus kusiroensis
Medium to thickly bedded arkosic wacke and shale with occaisional beds of pebbly conglomerate.  Flute casts and complete Bouma sequences
Ksg
Mainly Upper Cretaceous rocks
Slate, argillite, graywacke, and conglomerate, thoroughly indurated, and generally highly metamorphosed.
Metamorphic
Kaguyak Formation
Late Cretaceous; Maestrichtian and Campanian
Measured thickness is 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 of unit, graywa
In general, fossils are sparse; however, in lower part of unit they are locally abundant.  Ammonites are most common and may range in size to as much as 1-m-across.  Fossils allow age assignment of latest Campanian and early Maestrichtian for Kaguyak.
Kc
Cape Current terrane of Connelly (1978)
Informal unit consisting principally of medium- to thick-bedded arkosic and lithic sandstone containing occaisional sections of vesicular pillow lava and pillow breccia.  Slightly metamorphosed and moderately deformed.  Contains two bodies of red pelagic
Coccoliths of indeterminate age and Late Cretaceous foraminifera in limestone
Khe
Herendeen Formation
Early Cretaceous; Barremian and Hauterivian
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
Inoceramus fragments form major component of formation, although complete specimens have only been found in the Mount Katmai area.  A belemnite similar to Acroteuthis sp. A (Jones and Detterman, 1966) was found in rocks of formation just east of Staniuko
AF008
Ku
Uyak Complex
Cretaceous
Lithologically chaotic assemblage of deep-sea rock types.  Includes: argilite and gray chert containing minor tuff; massive arkosic sandstone; pillowed and massive greenstone; bedded radiolarian chert; minor limestone; and tuffaceous argillite.
Kuf
Uyak Formation
Triassic
Principally black shale and local schistose tuff.  A few shale and sandstone graded beds occur.  Middle third of Formation contains many beds of pillow basalt and red chert and the upper characterized by thick layers of light-gray chert.  Thin limestone
Triassic marine fossils in lower limestone lense
KR007
Lithologically chaotic assemblage of deep-sea rock types.  Includes argillite and gray chert, massive arkosic sandstone, pillowed and massive greenstone, rhythmically bedded radiolarian chert, minor limestone, and tuffaceous argillite.
sgs
Mainly Triassic and Jurassic rocks possibly some Paleozoic or older rocks
Mesozoic and Paleozoic?
A structurally complex group of rocks of great lithologic diversity.  Includes ellipsoidal lava with associated slate, thin-bedded chert and slate, calcareous slate, graywacke, and limestone, and their metamorphic equivalents, represented by greenstone s
KJm
McHugh Complex
Weakly metamorphosed siltstone, graywacke, arkose and conglomeratic sandstone; greenstone (mostly basaltic), chert and argillite
AF011
Kuu
Uyak Complex- Gabbroic and ultramafic rocks
Lithologically chaotic assemblage of deep-sea rock types.  Gabbroic and ultramafic rock, including layered gabbro, clinopyroxenite, dunite, and plagioclase peridotite.
Uyak Complex - gabbroic and ultramafic rocks
Jn
Naknek Formation
Late Jurassic; Tithonian to Oxfordian
Originally named Naknek Series by Spurr (1900, p. 169-171, 179, 181) for exposures at Naknek Lake.  Detterman and others (1996; see also, Detterman and Hartsock, 1966; Martin and Katz, 1912) have subdivided unit into five members on Alaska Peninsula.
Megafossils, particularly pelecypod Buchia (Detterman and Reed, 1980, p. B38; J.W. Miller, written communs., 1982-88), are common, and fauna, which also includes ammonites, indicate age range of Oxfordian to late Tithonian (Late Jurassic).
Jns
Naknek Formation -- Sandstone member
Late Jurassic; late Oxfordian to Kimmeridgian
Upper part consists of up to 759 m of mainly thin-bedded fine-grained, olive-brown sandstone.  Lower part mainly massive to thick bedded medium- to coarse-grained arkosic sandstone
Buchia fossils are  in upper of unit, sparse ammonites.
Jnn
Naknek Formation -- Northeast Creek Sandstone Member
Late Jurassic; 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.  Sandstone is typically thick bedded and crossbedded and contai
Fossils are uncommon in unit although carbonaceous debris is common locally.
Naknek Formation -- Northeast Creek Sandstone member
Jnst
Naknek Formation -- Siltstone member
Medium- to dark-olive-gray, slightly calcareous to siliceous and micaceous siltstone with nodules, concretions, and thin, lenticular limestone beds
Main fossils present are Buchia Concentrica and a few ammonites.
Naknek Formation -- Snug Harbor Siltstone Member
Late Jurassic; 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.  Limestone nodules are locally abundant, and limestone beds are present in some s
It is lowest abundantly fossiliferous member of Naknek; main fossils present are of genus Buchia.
Jni
Naknek Formation -- Indecision Creek Sandstone Member
Late Jurassic; Tithonian and Kimmeridgian
Consists of medium-gray, fine- to medium-grained arkosic sandstone and siltstone.  It is thin bedded to massive; where bedded, it is locally crossbedded.  Fresh biotite and hornblende are minor, but important, components of sandstone, as they are interpr
Indecision Creek Sandstone Member is abundantly fossiliferous; however, fossils are restricted almost exclusively to pelecypods of genus Buchia.
Jnc
Naknek Formation -- Conglomerate member
Late Jurassic
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
Naknek Formation -- Chisik Conglomerate member
Late Jurassic (Oxfordian)
Limited to northern half of Alaska Peninsula, unit is composed of 614 m of massive to thick-bedded conglomerate and interbedded, crossbedded, clean quartzose sandstone.  Clasts range in size from maximum of 120 cm at bottom to 15 cm at top.  Clast compos
Jss
Shelikof Formation -- Sandstone member
Middle Jurassic; Callovian
Massive to thick-bedded, medium to coarse-grained, dark-green to gray volcanogenic sandstone containing abundant magnetite grains  (Note, owing to rapid lateral facies changes, informal subdivisions of Capps (1923) have been found impractical for mapping
Megafauna are locally abundant in Shelikof, although, in general, formation is unfossiliferous.  Vast majority of fossils collected from formation are ammonites of Callovian age; however, a few specimens suggest a Bathonian(?) age for some rocks (Allaway
Jk
Kialagvik Formation
Middle and Early Jurassic; Bajocian to Toarcian
Olive-gray to green, medium-bedded, fine- to medium-grained graywacke, mudstone, siltstone, and shale; local lenses of volcanic pebble conglomerate.
Shallow-water deposits of Kialagvik Formation are abundantly fossiliferous; most megafauna indicate age of early and middle Bajocian, although overall age range of fossils collected from unit is late Toarcian to Callovian (Imlay, 1984; see also, Detterma
Jt
Talkeetna Formation
Early Jurassic
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.
Age of unit, Early Jurassic (Hettangian and early Sinemurian), is based on abundant megafauna; however, this megafauna is present in great abundance in only a few horizons and may represent mass kills as a result of volcanic eruptions (Detterman and othe
Js
Schist of Kodiak Island
Jurassic
Thinly layered and complexly folded quartz-mica schist, greenschist, crossite-epidote schist, and epidote amphibolite.
Trls
Limestone
Late Triassic; Norian
Medium- to thick-bedded dark-gray limestone and thin to shaly bedded light tan limestone; locally contains massive chert-pebble and limestone-cobble conglomerate.  Interbedded with basalt flows, volcanic rubble flows and agglomerate.
Locally abundant pelecypods and ammonites yield Norian age
A 46-m-thick columnar-jointed basalt flow or sill from upper part of section has yielded a potassium-argon age of 197? +/- 12 Ma (Wilson and Shew, 1992); however, it remains to be determined whether basalt is sill from overlying Early Jurassic Talkeetna
Trk
Kamishak Formation
Detterman and Reed (1980) divided unit into three members, in descending order, Ursus Member, middle member, and Bruin Limestone Member.  On Alaska Peninsula (see inset A, pl. 1), Triassic limestone strata was assigned to Bruin(?) Limestone Member of Kam
Fossils that have been found yield Norian age (Detterman and Reed, 1980; C.D. Blome, U.S. Geological Survey, oral commun., 1981).
Trss
Shuyak Formation, sedimentary member
Late Triassic
Volcaniclastic sequence consisting of thin- to medium-bedded lithic sandstone containing lesser conglomerate, argillite, and siliceous tuff intruded by mafic dikes and sills (unit Trm of Connelly, 1978).
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 determination on flow unit was 197 +/- 12 Ma (Wilson and Shew, 1992); age is thought to be minimum age, as it is younger than stratigraphic position suggests.
Trm
Mafic dikes, sills, and plugs
Triassic?
Diabasic bodies intruding Shuyak Formation
Trsv
Shuyak Formation, volcanic member
Vesicular pillowed greenstone, locally containing beds of pillow breccia agglomerate, tuff, and argillite.  Greenstone is tholeiitic in composition.
Ja
Afognak Pluton
Hornblende diorite and hornblende quartz diorite
K-Ar ages on hornblende of 192.7, and 188.4 Ma; U-Pb age of about 210 Ma
Pls
middle Permian
Consists of 40 m of massive, light-gray, crystalline 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 dip about 40ø northwest, which p
Hanson (1957) reported age of late middle Permian (early Guadalupian) for these rocks on the basis of poorly preserved and silicified coral, brachiopod, and foraminifer fossils.
Permian; early Guadalupian
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 di
Hanson (1957) reported age of late mid-Permian (early Guadalupian) for these rocks on the basis of poorly preserved and silicified coral, brachiopod, and foraminifer fossils.
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 and were not examined during this study (see inset A, pl. 1).  Well-developed j