nm
Areas not mapped
unknown
Areas not to be filled that lie within coverage, typically not mapped
Gehrels, G.E., and Berg, H.C., 1992, Geology of southeastern Alaska:  U.S. Geological Survey Miscellaneous Investigation Series Map I-1867, scale 1:600,000.
Qs
Surficial sedimentary deposits
Quaternary
Unnamed lacustrine, fluvial, colluvial, glacial, beach, and marine deposits that are found in many areas of southeastern Alaska
QTv
Volcanic rocks
Quaternary and Tertiary
Edgecumbe Volcanics (basalt, andesite, and dacite) on Kruzof Island (Loney and others, 1975) and unnamed basaltic to rhyolitic rocks on islands west of Prince Wales Island (Eberlein and others, 1983), on Revillagigedo Island and mainland to east (Berg an
Ts
Sedimentary rocks
Tertiary
Nonmarine sandstone, shale, and conglomerate (Kootznahoo Formation) in the Zarembo-Kuiu Islands region (Brew and others, 1984) and on Admiralty Island (Lathram and others, 1965), and marine calcareous sandstone and siltstone (Topsy Formation) of Miocene
QTs
Pleistocene to Miocene marine mudstone, siltstone, sandstone, and conglomerate (Yakataga Formation) northwest of Cross Sound (Plafker and Addicott, 1976; George Plafker, written commun., 1984)
Tsv
Sedimentary and volcanic rocks, undivided
Unnamed carbonaceous shale, sandstone, and conglomerate of probable Paleogene age and subordinate Oligocene volcanic rocks near Haines (George Plafker, written commun., 1984; E.C. Robertson, written commun., 1984; Campbell and Dodds, 1983).
Tv
Oligocene and Eocene basalt and andesite (Admiralty Island Volcanics) on Admiralty Island (Lathram and others, 1965); unnamed Oligocene basaltic rocks on islands in Icy Strait (Hudson and others, 1982); basaltic rocks (Cenotaph Volcanics) of Miocene and
Tgr
Granite
Miocene and Oligocene
Biotite +/- hornblende +/- pyroxene granite, alkali granite, quartz monzonite, and subordinate syenite, granodiorite, and diorite. Unit consists of (1) stocks on mainland southeast of Revillagigedo Island that yield potassium-argon apparent ages of early
Tgb
Gabbro
Layered and locally zoned bodies of two-pyroxene +/- olivine +/- biotite +/- hornblende +/- quartz gabbro and subordinate troctolite, peridotite, leucogabbro, diorite, and tonalite. Unit consists of stocks on Revillagigedo Island and adjacent mainland (B
Tgd
Granodiorite
Oligocene and Eocene
Biotite +/- hornblende +/- muscovite +/- garnet granodiorite, granite, quartz monzonite, tonalite, and quartz diorite. Unit consists of muscovite- and locally garnet-bearing granodiorite, granite, and tonalite on Baranof and Chichagof Islands and in Glac
Tg
Eocene
Biotite-dominant, hornblende- and sphene-bearing granodiorite and subordinate quartz monzonite, quartz diorite, and leucogranite found in Coast Mountains (Berg and others, 1978, 1988; Elliott and Koch, 1981; Brew and others, 1984; Webster, 1984; Brew and
Tgt
Granodiorite and tonalite
Paleocene
Biotite-dominant, hornblende-bearing granodiorite and tonalite containing local foliation and layering. Uranium-lead (zircon) data indicate emplacement during Paleocene time (Gehrels and others, 1984). Found in Coast Mountains east of Petersburg (Brew an
TKg
Paleocene and Cretaceous
Diverse assemblage of generally foliated and layered granodiorite, quartz monzonite, tonalite, and their metamorphic equivalents. May include a significant component of pre-Tertiary metasedimentary and metavolcanic rocks (pTmsv) in some areas. Where reco
TKt
Tonalite
Hornblende -dominant, biotite-bearing tonalite and subordinate quartz diorite found as steeply dipping, foliated, and locally lineated sills in Coast Mountains (Brew and Ford, 1981). Found near Ketchikan (Berg and others, 1978, 1988; Elliott and Koch, 19
KJv
Cretaceous
Andesite to basaltic flows, flow breccia, agglomerate, and tuff (generally containing conspicuous clinopyroxene phenocrysts), subordinate graywacke and mudstone, and regionally metamorphosed and deformed equivalents of these strata. Greenschist facies me
Kgt
Small plutons to batholiths of granodiorite, tonalite, and subordinate quartz monzonite to quartz diorite and diorite. Most bodies contain biotite and hornblende, many have magmatic epidote and garnet and are plagioclase porphyritic, and some contain pyr
Kg
A heterogeneous suite of plutons consisting primarily of biotite, hornblende, magnetite +/- pyroxene +/- garnet granodiorite and subordinate quartz monzonite, tonalite, trondhjemite, and quartz diorite. On Chichagof Island there plutons are associated wi
Kdb
Diorite and gabbro
Hornblende diorite and gabbro that grades laterally into granodiorite and quartz diorite (unit Kgt). Potassium-argon ages are Late Cretaceous (Redman and others, 1984). Found in the Haines area
Kum
Ultramafic rocks
Ultramafic intrusive bodies of magnetite-bearing hornblende clinopyroxenite and subordinate dunite, peridotite, and hornblendite (Taylor, 1967). Several complexes are concentrically zoned from a core of dunite to rocks containing progressively less olivi
Kd
Diorite
Primarily hornblende +/- biotite +/- clinopyroxene diorite and subordinate quartz diorite and gabbro. Generally found in association with Early Cretaceous granodiorite (unit Kg) and gabbro (unit Kgb). Found on Prince of Wales Island (Eberlein and others,
Kgb
Primarily clinopyroxene (generally augite) +/- hornblende +/- biotite +/- olivine gabbro, leucogabbro, and subordinate norite, syenite, and pyroxenite. Found on Prince of Wales Island (Eberlein and others, 1983), Kuiu Island (Brew and others, 1984), and
KJs
Cretaceous and Jurassic
Marine graywacke and mudstone, subordinate conglomerate and andesitic to basaltic volcanic rocks, minor limestone, and regionally metamorphosed and deformed equivalents of these strata. Metamorphic grade generally increase from subgreenschist facies or n
KJsv
Moderately deformed and metamorphosed graywacke, mudstone, sandstone, and andesitic to basaltic rocks. Strata belong to the Shelter Formation in southern Lynn Canal (Barker, 1957) and are undifferentiated correlatives of the Treadwell Slate (unit KJs), t
Ksm
Includes sedimentary and metasedimentary rocks that are similar in structural and metamorphic characteristics to rocks in the Cretaceous sedimentary and volcanic melange unit (Ksvm). Common lithic types include dark-gray phyllite, light-gray quartzite, a
Ksv
Interbedded sedimentary and volcanic rocks, and their metamorphosed equivalents, that are correlative and continuous with Cretaceous sedimentary (Ks) and volcanic (Kv) rocks. Found north of Cross Sound (Brew and others, 1978; Brew and Morrell, 1979; Plaf
Ks
Sandstone and mudstone turbidites and subordinate conglomerate (Sitka Graywacke) on Baranof, Chichagof, Kruzof, and Yakobi Islands (Loney and others, 1975; Johnson and Karl, 1985; Decker, 1980) and regionally metamorphosed carbonaceous siltstone, volcano
Kv
Basalt and basaltic tuff north of Cross Sound that are deformed and regionally metamorphosed as high as amphibolite facies (Brew and others, 1978; George Plafker, written commun., 1984). Common rock types include schist, gneiss, and amphibolite (Brew and
KJgb
Two-pyroxene gabbro and subordinate hornblende +/- biotite gabbro and diorite. These intrusive rocks generally found adjacent to and intruded by Early Cretaceous zoned ultramafic bodies (unit Kum). Found on mainland near Myers Chuck (Ruckmick and Noble,
Ksvm
Consists of (1) blocks as much as several kilometers in length of marine sedimentary and volcanic rocks, and their metamorphic equivalents, that are bounded by fault or shear zones; and (2) blocks as much as several tens of meters in length of marine sed
Kvm
Includes mafic volcanic and metavolcanic rocks that resemble rocks in the Cretaceous sedimentary and volcanic rocks melange unit (Ksvm) in structural and metamorphic characteristics. Common lithic types include greenstone, greenschist, and minor phyllite
KDsd
Cretaceous to Devonian
Deformed, disrupted, and metamorphosed graywacke, siltstone, mudstone, and subordinate chert, limestone, and volcanic and intrusive rocks that belong to a belt of regionally disrupted rocks in the Kupreanof-Etolin Islands area. Common metamorphic rock ty
KDvd
Deformed, disrupted, and metamorphosed mafic to intermediate and minor felsic volcanic rocks that belong to a belt of regionally disrupted rocks in the Kupreanof-Zarembo Islands area.  Rocks generally metamorphosed to greenschist and greenstone.  Presenc
KJd
Metamorphosed and moderately deformed diorite and subordinate quartz diorite and gabbro on Annette Island, Revillagigedo Island, and mainland to northwest (Berg and others, 1978, 1988). A small quartz diorite body near northern Annette Island yielded a C
Jt
Jurassic
Biotite and hornblende tonalite and quartz diorite on Chichagof Island that yielded a Middle Jurassic potassium-argon (hornblende) apparent age (Loney and others, 1975)
Jgr
Peralkaline aegerine and arfvedsonite granite (Bokan Mountain Granite) on southern Prince of Wales Island (MacKevett, 1963) that yielded Jurassic potassium-argon (Lanphere and others, 1964), uranium-lead (zircon) (Saint-Andre and others, 1983), and rubid
Trg
Triassic
Hornblende and biotite granodiorite and minor quartz diorite (part of Texas Creek Granodiorite of Berg and others, 1977) norheast of Revillagigedo Island (Berg and others, 1978, 1988) that yielded a latest Triassic potassium-argon (hornblende) apparent a
JTrd
Jurassic and (or) Triassic
Hornblende and biotite diorite (Jualin Diorite) along east shore of Lynn Canal (Knopf, 1911; Redman, 1984a). The diorite produces a hornfelsic aureole in adjacent metasedimentary and metavolcanic rocks of probable Triassic or Permian age (unit KPsv) and
Trsc
Clastic sedimentary and carbonate rocks, undivided
Unnamed, moderately deformed and metamorphosed graphitic limestone and slate of late Ladinian (latest Middle Triassic) age on Revillagigedo Island (Silberling and others, 1982). On the basis of regional stratigraphic relations and slightly older age, Sil
Trgb
Two-pyroxene gabbro on Duke Island (Irvine, 1974) and Percy Islands (Berg and others, 1978, 1988) that yields a Late Triassic uranium-lead (zircon) apparent age (Gehrels and others, 1987)
Trb
Basaltic rocks
Basaltic flows and flow breccia (Goon Dip Greenstone) on Chichagof and Yakobi Islands that were deposited, at least in part, in subaerial environments (Loney and others, 1975; Johnson and Karl, 1985) and unnamed basalt near Haines (Plafker and Hudson, 19
Trs
Upper Triassic conglomerate, limestone, and calcareous siltstone and sandstone (Burnt Island Conglomerate) west of Etolin Island (Karl, 1984) and on northwestern Kupreanof Island (Muffler, 1967); unnamed silty limestone of Late Triassic age on small isla
Trsv
Black shale, shaly limestone, siltstone, sandstone, conglomerate, and limestone; felsic, intermediate, and mafic flows; and minor black chert.  Rocks vary from relatively unmetamorphosed to as high as greenschist facies. Common rock types in higher grade
Trc
Carbonate rocks
Massive to thick-bedded limestone and minor dolomite in most areas, but in Keku Strait unit includes thin-bedded, dark-gray limestone, and on Chichagof Isalnd unit consists of massive white to gray marble (Whitestripe Marble). Diagnostic fossils from lim
Trv
Volcanic rocks (rhyolitic to basaltic)
Basaltic pillow flows, pillow breccia and breccia; rhyolitic tuff with calcareous interbeds, flow breccia, and banded ash-flow tuff, and subordinate andesitic breccia and aquagene tuff. Rocks in most areas are moderately recrystallized and deformed. Foss
TrPc
Triassic and (or) Permian
Unfossiliferous marble on mainland northwest of Revillagigedo Island (H.C. Berg, unpub. data, 1975) and on and northeast of Etolin Island (Brew and others, 1984). Age inferred from similarity with Triassic and Permian marble layers included in units of C
KPs
Cretaceous to Permian
Carbonaceous shale, mudstone, and graywacke; subordinate limestone, chert, conglomerate, and mafic volcanic rocks; minor felsic volcanic rocks; and the metamorphosed and deformed equivalents of these rocks. Regional metamorphic grade in these strata and
KPsv
Shale, mudstone, graywacke, andesitic or basaltic rocks, subordinate chert and carbonate rocks, and the regionally metamorphosed equivalents of these strata. Nature and age of metamorphism is similar to that described above for Cretaceous to Permian sedi
KPv
Andesitic or basaltic flows and locally fragmental rocks, subordinate clastic strata and carbonate, and the metamorphosed and deformed equivalents of these rocks. Regional metamorphism of these strata is similar to that described above for Cretaceous to
TrOsv
Triassic to Ordovician
Clastic sedimentary rocks, subordinate mafic to felsic volcanic rocks, thin- to thick-bedded gray carbonate, chert, and minor ultramafic rocks that have been regionally metamorphosed to slate, phyllite, greenschist, schist, gneiss, and marble in many are
TrPsv
Triassic and Permian
Andesitic to basaltic pillow flows, breccia, and tuff; felsic tuff; graywacke, mudstone, shale, chert, conglomerate, and carbonate; and the metamorphic equivalents of these strata. Unit consists of the Barlow Cove Formation (Barker, 1957) and strata belo
JMsv
Jurassic to Mississippian
Diverse assemblage of sedimentary and volcanic rocks and their metamorphic equivalents. Found near British Columbia-Alaska border northeast of Revillagigedo Island (Berg and others, 1978, 1988; Elliott and Koch, 1981) and east of Juneau (Souther and othe
KPsvc
Clastic sedimentary, volcanic, and carbonate rocks
Unnamed fossiliferous argillite of Cretaceous age; variably metamorphosed chert, tuffaceous sandstone, felsic tuff, argillite, and light-gray, thin-bedded limestone of Mesozoic or Paleozoic age; highly sheared metasedimentary, metavolcanic, and granodior
Pc
Permian
Consists of (1) greenschist-facies, massive to thin-bedded marble of Early Permian age on Revillagigedo Island (Silberling and others, 1982; Berg and others, 1978, 1988) and of Permian (?) age on mainland east of Admiralty Island (Brew and Grybeck, 1984)
Ps
Black argillite, graywacke, calcareous siltstone, chert, and minor basaltic rocks, limestone, and conglomerate. Unit consists of (1) part of the Halleck Formation of Early Permian age near Keku Strait (Muffler, 1967; Brew and others, 1984; Jones and othe
Pv
Lower Permian basalt (part of the Halleck Formation) on northern Kuiu Island (Muffler, 1967) and unnamed Permian basaltic (?) rocks northeast of Glacier Bay (Brew and others, 1978). Age constrained by interbedded Lower Permian clastic strata (unit Ps) on
PPasy
Syenite
Permian and (or) Pennsylvanian
Syenite on Sukkwan Island that contains biotite +/- amphibole +/- aegerine +/- augite and yielded potassium-argon apparent ages of Early Permian (hornblende) and Late Pennsylvanian (biotite) (Eberlein and others, 1983). This body is apparently correlativ
MDsv
Mississippian and Devonian
Tuffaceous argillite and graywacke and subordinate chert, limestone, and andesitic volcanic rocks (Cannery Formation) on northern Kupreanof Island (Muffler, 1967; Brew and others, 1984). Fossils are Late Devonian and Early and Late Mississippian in age (
Pac
Pennsylvanian
Massive limestone and minor dolomite containing light-gray chert nodules (Ladrones Limestone) on west-central Prince of Wales Island (Eberlein and others, 1983) and unnamed, medium-bedded to massive crinoidal limestone on northern Kuiu Island (Brew and o
Pas
Middle and Lower Pennsylvanian sandstone and siltstone containing minor limestone and chert-pebble conglomerate (Klawak Formation). Unit found on west-central Prince of Wales Island (Eberlein and others, 1983)
PaDsv
Pennsylvanian to Devonian
Saginaw Bay Formation on Kuiu Island. From youngest to oldest, unit consists of silty limestone, calcareous chert and limestone, black chert, and massive aquagene tuff and pillow breccia (Muffler, 1967). Silty limestone and calcareous chert and limestone
Mc
Mississippian
Thin- to thick-bedded, dark-gray limestone, subordinate beds and nodules of light-gray chert, and minor shale and gypsum, unit consists of  the Peratrovich Formation on western Prince of Wales Island (Eberlein and others, 1983) and the Iyoukeen Formation
DOc
Devonian to Ordovician
Carbonate rocks that were metamorphosed to thin- to thick-bedded, dark-gray to white marble. Consists of unnamed rocks on northeastern Chichagof Island and in Glacier Bay area. Loney and others (1975) suggest that marble on Chichagof Island was derived p
TrOc
Carbonate rocks regionally metamorphosed to gray marble (MacKevett and others, 1974; Lathram and others, 1959; Brew and Ford, 1985; Redman and others, 1985). Fossils of Pennsylvanian (?) or Permian (?), Paleozoic (?), and Devonian (?) or Silurian (?) age
Scg
Conglomeratic rocks
Silurian
Polymictic pebble and cobble conglomerate and subordinate sedimentary breccia, olistostromal deposits, sandstone, graywacke, mudstone, and limestone. Clasts consist of porphyritic andesite, limestone, graywacke, mudstone, granitic to gabbroic intrusive r
Ss
Graywacke and mudstone turbidites and subordinate olistostromal deposits, layers, and lenses of limestone, and conglomerate. Unit consists of (1) most of the Bay of Pillars Formation (Upper and Lower Silurian) on northern Prince of Wales Island and Kuiu
SOsv
Silurian and Ordovician
Mudstone and graywacke turbidites, basaltic and andesitic volcanic rocks, and metamorphic equivalents of these strata. Unit consists of (1) part of the Descon Formation on Prince of Wales Island (Eberlein and others, 1983); (2) metasedimentary and metavo
SOs
Mudstone and graywacke turbidites, subordinate conglomerate, sandstone, and shale, and minor limestone, chert, and basalt flows and breccia. Unit consists of (1) unnamed strata of probable Early and Silurian to Middle Ordovician age on Sukkwan and Dall I
SOv
Basaltic pillow flows, pillow breccia, and aquagene tuff; massive andesite pyroclastic breccia; felsic breccia and tuff; subordinate interbeds of mudstone and graywacke turbidites and metamorphic equivalents of these strata. Unit consists of (1) mafic to
Sst
Syenite and trondhjemite
Consists of (1) leucocratic biotite +/- aegerine +/- arfvedsonite +/- garnet syenite and subordinate leucodiorite on southern Prince of Wales Island (Gehrels and Saleeby, 1986, 1987a); (2) biotite and hornblende trondhjemite on Annette and Gravina Island
Sv
Mafic to intermediate volcanic breccia, agglomerate, and flows and greenschist and greenstone derived from these rocks. Found with Silurian sedimentary (Ss) and carbonate rocks (Sc) belonging to the Bay of Pillars Formation on southern Kuiu Island (Brew
SOum
Pyroxenite, hornblendite, and related ultramafic rocks on southern Prince of Wales Island (MacKevett, 1963; Gehrels and Saleeby, 1986, 1987a), on southern Dall Island (G.E. Gehrels, unpub. data, 1984), and on east-central Prince of Wales Island (Loney an
SOsvc
Clastic sedimentary, volcanic, and carbonate rocks, undivided
Interbedded graywacke, mudstone, mafic to felsic volcanic rocks, and limestone that have been regionally metamorphosed as high as greenschist facies (Gehrels and Saleeby, 1987b; G.E. Gehrels, unpub. data, 1984). Found along west coast of Dall Island and
Dsv
Devonian
Siltstone, shale, volcanogenic graywacke, conglomerate, and minor limestone that are interbedded with basaltic pillow flows, breccia, and aquagene tuff. Unit consist of the Coronados Volcanics (Devonian), the Devonian (?) St. Joseph Island Volcanics, and
DSc
Devonian and Silurian
Thin, discontinuous, unfossiliferous limestone layers associated with Devonian and Silurian volcanic rocks (DSv) in the Chilkat Range (Lathram and others, 1959; Brew and Ford, 1985)
Dcg
Conglomerate and sedimentary breccia interbedded with sandstone, siltstone, shale, and minor graywacke, limestone, and volcanic rocks. Sedimentary structures and presence of red beds and thick sections of coarse conglomerate suggest that strata in Prince
Dc
Thin-bedded to massive, gray limestone and minor shale interbeds. Unit consists of (1) the Upper and Middle (and probably upper Lower) Devonian Wadleigh Limestone in west-central Prince of Wales Island region (Eberlein and others, 1983; Savage and Gehrel
Ds
Siltstone, shale, sandstone, graywacke, and subordinate limestone breccia, arkose, conglomerate, and volcanic rocks. Unit consists of (1) the Lower Devonian Karheen Formation in the Annette-Gravina Islands area (Gehrels and others, 1987) and on southern
DSsc
On north-central Prince of Wales Island unit consists of unnamed limestone, sandstone, calcareous mudstone, and polymictic conglomerate interpreted to be facies equivalents of the Silurian Heceta Limestone (unit Sc), associated Silurian clastic strata (u
Sc
Massive, thin- to thick-bedded, locally reefoidal, light-gray limestone and subordinate shale and polymictic conglomerate. Unit consists of (1) unnamed Silurian limestone and marble on Dall and Long Islands (Eberlein and others, 1983; Gehrels and Saleeby
DSv
Unnamed Devonian or Silurian andesitic (?) volcanic rocks found in a fault slice on northern Kuiu Island (Muffler, 1967; Brew and others, 1984); unnamed Devonian and Silurian basaltic and (or) andesitic rocks in Glacier Bay (Brew and others, 1978); and u
Dv
Basaltic and subordinate andesitic pillow flows, breccia, aquagene tuff, and minor sedimentary interbeds. Unit consists of (1) unnamed basaltic-andesitic pillow flows and breccia (Lower Devonian) on small islands south of Annette Island (Gehrels and othe
DOsv
Graywacke, mudstone, shale, limestone, and subordinate mafic to intermediate volcanic rocks that have been metamorphosed in most areas to hornfels, slate, phyllite, schist, amphibolite, marble, gneiss, and granofels. Unit consists of unnamed rocks on nor
SOq
Quartz diorite
Consists of (1) Late and Middle Ordovician diorite and quartz diorite and Early Silurian to Late Ordovician biotite quartz monzonite on Prince of Wales Island (Gehrels and Saleeby, 1987a; Eberlein and others, 1983; Saleeby and others, 1984; Lanphere and
Ogb
Ordovician
Hornblende gabbro and subordinate hornblende pyroxenite and hornblendite on Sukkwan Island that yielded a Middle Ordovician potassium-argon apparent age (Eberlein and others, 1983) and an undated metagabbro on southern Dall Island interpreted to be corre
Cdg
Diorite and granodiorite
Cambrian
Foliated and metamorphosed hornblende diorite and biotite +/- hornblende granodiorite on east-central Prince of Wales Island and on southern Gravina Island that yielded Late and Middle Cambrian preliminary uranium-lead (zircon) apparent ages (Gehrels and
pOmsv
Metasedimentary and metavolcanic rocks
pre-Ordovician
Metasedimentary and metavolcanic rocks derived from pre-Ordovician basaltic to andesitic pillow flows, pillow breccia, and tuff breccia, volcanoclastic graywacke and mudstone, and minor limestone and felsic volcanic breccia and tuff during regional green
pOmc
Metacarbonate rocks
Metacarbonate rocks derived from pre-Ordovician carbonate rocks during regional greenschist- and local amphibolite-facies metamorphism. Found as thin to thick marble layers and lenses intercalated with pre-Ordovician metasedimentary and metavolcanic rock
pTmsv
pre-Tertiary
Metasedimentary and metavolcanic rocks derived from pre-Tertiary sedimentary and volcanic rocks during regional amphibolite- and local granulite- facies metamorphism. Common rock types include pelitic, semipelitic, and quartzofeldspathic schist and gneis
pTmc
Metacarbonate rocks derived from pre-Tertiary carbonate rocks and carbonate-rich clastic strata during regional amphibolite- and local granulite-facies metamorphism. Found as discontinuous marble lenses, as thick continuous marble layers, and as calc-sil