Geologic Map of the Wrangell-Saint Elias National Park and Preserve, 

Alaska

Compiled by Donald H. Richter, Cindi C. Preller, Keith A. Labay, and Nora B. Shew

Pamphlet to accompany

Scientific Investigations Map 2877

2006

U.S. Department of the Interior

U.S. Geological Survey


GEOLOGIC NOTE

INTRODUCTION

Wrangell-Saint Elias National Park and Preserve, the 

largest national park within the U.S. National Park Service 

system, extends from the northern Pacific Ocean to beyond 

the eastern Alaska Range into interior Alaska. It features 

impressively spectacular scenery such as high and craggy 

mountains, active and ancient volcanoes, expansive ice 

fields, immense tidewater glaciers, and a myriad of alpine 

glaciers. The park also includes the famous Kennecott 

Mine, a world-class copper deposit that was mined from 

1911 to 1938 (fig. 1), and remnant ghost town, whic

now a National Historic Landmark.

PREVIOUS WORK

Geologic investigations encompassing Wrangell-Saint 

Elias National Park and Preserve began in 1796, with Dmitriv Tarkhanov, a Russian mining engineer, who unsuccessfully ventured up the Copper River in search of rumored

copper (Grinev, 1987, as cited in Hunt, 1996). Lieutenan

H.T. Allen (1897) of the U.S. Army made a successful

epic summer journey with a limited military crew up the 

Copper River in 1885, across the Alaska Range, and down

the Tanana and Yukon Rivers. Allen’s crew was supported 

by a prospector named John Bremner and local Eyak and 

Ahtna native guides whose tribes controlled access into 

the Copper River basin. Allen witnessed the Ahtnas’ many 

uses of the native copper. His stories about the copper 

prompted prospectors to return to this area in search of 

the rich copper ore in the years following his journey. The 

region boasts a rich mining and exploration history prior to 

becoming a park in 1980 (fig. 2). Several U.S. Geological

Survey geologists have conducted reconnaissance surveys 

in the area since Allen’s explorations. This map is the result 

of their work and is enhanced by more detailed investigations (fig. 3, on map sheet), which began in the late 1950’s

and are still continuing. For a better understanding of the 

processes that have shaped the geology of the park and a 

history of the geologic investigations in the area, we recommend U.S. Geological Survey Professional Paper 1616

“A Geologic Guide to Wrangell-Saint Elias National Park 

and Preserve, Alaska”, an exceptionally well illustrated 

and informative book by Gary R. Winkler, 2000.

BEDROCK TERRANES

Geologically, the park consists of a collage of seven 

tectonostratigraphic terranes that formed south in the equatorial Pacific Ocean and rafted northward on oceanic plates, 

eventually accreting to Alaska and the North American continent (fig. 4, on map sheet). Each terrane features a distinct 

Figure 1. The Kennecott Mine mill building and railroad cars full of copper ore from the Bonanza and 

Jumbo Mines of the Kennecott mining district, circa 1920. View to northeast. Photo courtesy of Geoff

Bleakley.
stratigraphy and is separated from neighboring terranes by 

major strike-slip or thrust faults.

The Windy terrane, exposed in the Alaskan interior 

north of the Denali Fault System and composed largely of 

Paleozoic metavolcanic and metasedimentary rocks, was 

the first to arrive; it accreted to the continent in Triassic and 

early Jurassic time (225–180 Ma)

Next to arrive was the Wrangellia composite terrane 

(Peninsular, Wrangellia, and Alexander(?) terranes), presently separated from the Windy terrane by the Denali Fault 

System, a series of strike-slip faults. During its journey 

north, the Wrangellia terrane merged with the Alexander(?) 

terrane before docking to the continent in early Cretaceous 

time (110–85 Ma). The Nutzotin Mountains sequence o

Berg and others, 1972, a thick marine flysch of Late Jurassic and Early Cretaceous age, and the short-lived Cretaceous

Chisana volcanic arc, formed in and along an oceanic trough 

next to the north edge of the Wrangellia composite terrane. 

As the composite terrane progressed north, the Nutzotin 

Mountain sequence eventually became the glue that attached 

Wrangellia to the continent.

The Alexander(?) terrane, located on the eastern edge 

of the park and extending into the neighboring Yukon 

Territory, Canada, stitched to the Wrangellia terrane by a 

Pennsylvanian monzonite-granite complex, is composed of 

early Paleozoic marble, schist, phyllite, and amphibolite.

Wrangellia, the principal terrane in the Wrangellia 

composite terrane, consists chiefly of a PennsylvanianFigure 2. Generalized locations of mines, prospects, mineral occurrences, and exploration oil and gas 

wells in or near Wrangell-Saint Elias National Park and Preserve. Mining information provided by the U.S. 

Geological Survey’s Alaska Resource Data File (http://ardf.wr.usgs.gov/). Oil and gas data provided by the 

State of Alaska Division of Oil and Gas (http://www.dog.dnr.state.ak.us/oil/). Shaded relief image courtesy 

of the National Park Service.

Oil and gas well

Mineral occurrence

Prospect

Mine

Wrangell-Saint Elias 

National Park and 

Preserve boundary

Map boundary

EXPLANATION

60° 00'

62° 00'

144° 00' 141° 00'

15 30 45 MILES

Gulf of Alaska

0
Permian volcanic arc, probably built on oceanic crust, overlain by a sequence of thick Triassic flood basalts, Triassic 

limestones, and Jurassic sedimentary rocks. It occupies the 

bulk of the region with magnificent volcanic edifices and 

broad glacial valleys.

The Peninsular terrane, buried by the deposits of ancient glacial Lake Atna (Nichols, 1989; Williams and Galloway, 1986) and exposed only locally west of the park

consists chiefly of a Jurassic volcanic arc that overlies the 

Wrangellia terrane.

Located south of the Wrangellia composite terrane and 

separated by the Border Ranges Fault, the Southern Margin 

composite terrane’s spectacular mountains consist of two distinct terranes: the Chugach and Prince William terranes.

The Chugach terrane’s towering peaks are composed 

largely of another, younger, marine flysch that formed in a 

deep oceanic trough, which arrived in the latest Cretaceous 

(about 67 Ma).

Following and separated by the Contact Fault System, 

the Chugach terrane was joined by the Prince William 

terrane (about 50 Ma), a Tertiary deep-sea fan and volcanic rock assemblage, home to the ecologically sensitive 

Copper River Delta.

Finally, arriving about 26 Ma and still actively accreting to the continent, is the Yakutat terrane, a series of Jurassic(?) and Cretaceous to late Tertiary sedimentary rocks 

that include minor amounts of oceanic volcanic rocks. The 

Yakutat terrane, host to some of the world’s largest glaciers (fig. 5, on map sheet), is separated from the northern 

terranes by the Chugach-Saint Elias Fault System and the 

Fairweather Fault.

QUATERNARY ACTIVItT

The Wrangell volcanic field forms much of the higher 

elevations of the Wrangell and Saint Elias Mountains. 

Initial volcanism began about 26 million years ago near 

the Alaska-Yukon border and progressed northwestward 

terminating at the spectacular Quaternary volcanoes of 

Mount Drum, Mount Wrangell, and Mount Sanford. The 

volcanic activity is related to the subduction of the Pacific 

Plate and coincided with the Yakutat terrane’s time of arrival. Subduction and associated volcanic activity largely 

ended about 200,000 years ago when much of the north 

movement of the Pacific Plate was then accommodated by 

right-lateral movement along the Denali Fault System, the 

Totschunda Fault System, and the Fairweather Fault; all 

strike-slip faults. As subduction mostly ceased, that part 

of Alaska south of the Denali-Totschunda Fault Systems, 

which includes most of Wrangell-Saint Elias National 

Park and Preserve, was largely coupled to the Pacific Plate. 

The latest activity to occur on the bounding faults was the 

shallow Magnitude 7.9 earthquake of November 3, 2002, 

whose epicenter was on the Denali Fault System northwest 

of the park. The ground rupture produced along the Denali 

and the Totschunda Fault Systems stretched into the park, 

as far southeast as the Nabesna River.

ACKNOWLEDGMENTS

Many of our colleagues have contributed to the compilation of this geologic map, for which we are grateful. 

E.M. MacKevett, Jr., George Plafker, H.R. Schmoll, G.R. 

Winkler, and L.A. Yehle all reviewed parts of the map; 

their efforts and comments contributed significantly to the 

map’s integrity. G.R. Winkler (bedrock) and H.R. Schmoll 

and L.A. Yehle (surficial deposits) reviewed the final product. Scott Starratt conducted the geologic names review. 

Carolyn Donlin edited the map. Rich Koch provided the 

digital cartography. Our most sincere appreciation extends 

to Logan Hovis, Suzanne McCarthy, D.S. Rosenkrans and 

the rest of the staff at Wrangell-Saint Elias National Park 

and Preserve, as well as many local residents of the Copper 

River basin, who helped in preparation of this map.

DESCRIPTIo of MAP U

[Some unit exposures are too small to distinguish for identification. While labeled when possible, 

all are attributed within the digital database.]

SURFICIAL DEPOSITS

Alluvial deposits

Qa Alluvium (Holocene)—In active streambeds and lowest terraces along larger 

streams and active alluvial fans. Chiefly well sorted gravel and sand; minor 

silt and boulders

Qao Older alluvium (Holocene and Pleistocene)—In higher terraces along larger 

streams and in inactive alluvial fans. Predominantly of Pleistocene age, but 

may include localized Holocene deposits. Chiefly well sorted gravel and 

sand; minor silt and boulders
Mass wasting deposits

Qu Slope deposits, undifferentiated (Holocene and Pleistocene)—Colluvium 

consisting of talus and small landslides, also includes small glacial, rock 

glacier, and alluvial deposits. Sand, gravel, boulders, diamicton, and rubble

Qcb Bluff colluvium (Holocene)—Occurs along high steep bluffs of the Copper 

River and its principal tributaries. Locally includes small areas of the 

Copper River deposits (Qcr) and the drift of older glaciations (Qg). 

Unsorted silt, sand, gravel, and boulders

Ql Landslide deposits (Holocene and Pleistocene)—Slumps, earth-debris 

flows, block glides, and debris avalanches. Diamicton and rubble

Glacial and glaciolacustrine deposits

Qrg Rock glacier deposits (Holocene)—Well-defined lobate forms that may include 

glacier ice cores. Chiefly blocks of rubble

Qag Drift of Alaskan glaciation (Holocene)—Neoglacial deposits of end, lateral, 

and ground moraines, kames and outwash proximal to present glaciers; 

includes small rock glaciers. Diamicton, local gravel, and sand

Qg Drift of older glaciations (Pleistocene)—Wisconsin glaciation and older end, 

lateral, and ground moraines, local kames, kame-like deposits, and outwash. 

Also includes the glaciolacustrine deposits (Qcr) near complex interface 

with glacial Lake Atna in lower Chitina River valley. Chiefly diamicton, 

local gravel and sand

Qcr Copper River deposits (Pleistocene)—Interbedded glaciolacustrine, glacial, 

and alluvial deposits. Includes deposits of glacial Lake Atna (Nichols, 

1989; Williams and Galloway, 1986); historically complex basin built fro

numerous lake stages in response to multiple glacial advances and retreats. 

Locally overlain by small fine-grained alluvium and pond deposits (Qfl). 

Interbedded with the Mount Wrangell valley-fill lavas (Qwwv) along western margin of Mount Wrangell, especially in Chetaslina River valley area. 

Clay-pebble silt and diamicton, containing local to regionally distributed 

beds of gravel and sand

Other unconsolidated deposits

Qfl Fine-grained deposits (Holocene)—In ponds, swamps, lagoons, and along 

low-gradient streams. Chiefly silt, clay, fine sand, peat, and other organic 

material

Qms Mineral spring deposits (Holocene)—Deposited by warm, Na-HCO3-rich, 

CO2-charged, saline spring waters forming the Klawasi Group (Shrub, 

Upper Klawasi, and Lower Klawasi) mud volcanoes (Motyka and others, 

1989) located west of Mount Drum. Also includes one or more inactive

deposits west of Capital Mountain; a methane-charged mineral spring found 

on Copper River’s east bank near Copper Center. Mud and clayey-silt

Qe Eolian deposits (Holocene)—Dunes on tops of river bluffs, windblown flats, 

and river bars. Includes informally named Bremner sand dunes, a large 

barchan field, located at confluence of Bremner and Copper Rivers. Finegrained sand

Qb Beach and delta deposits (Holocene)—Wave-deposited, coarse-grained material and driftwood along seacoast; fine-grained sediment in mud flats of 

Copper River Delta; and marine uplift terraces. Successive spit-building 

episodes of progressive gradation are preserved in beach sequences along 

coastal lowland between Cape Yakataga and Bering Glacier. Boulders, 

gravel, sand, and silt
WRANGELL VOLCANIC FIELD

This Oligocene to Holocene regional province covers more than 10,000 km2 in the Wrangell

and Saint Elias Mountains built by predominantly large non-explosive shield eruptive 

centers and summit calderas with a minor sedimentary base deposit. The Wrangell Lava 

collectively forms the entire volcanic field of effusive flows, tuffs, breccias, lahar deposits, 

dikes, and domes. The sedimentary nonmarine Frederika Formation was deposited prior to 

and during early stages of volcanism locally in southern Wrangell Mountains. Individual 

volcanic descriptions and ages (Richter and others, 1990) can be found in U.S. Geological

Survey Bulletin 2072, “Guide to the Volcanoes of the Western Wrangell Mountains, Alaska: 

Wrangell-St. Elias National Park and Preserve” (Richter and others, 1995

Individual volcanic eruptive centers

Mount Wrangell volcano (Holocene and Pleistocene, 0.65 Ma and 

younger)—Enormously bulky massive broad active shield; non-explosive, 

ice-filled caldera in summit area. Hundreds of voluminous andesitic lavas 

flowed for 650,000 years, concluding 25,000 years ago; one or two undated 

flows might be younger. As the only currently active volcano, present activity is limited to frequent steam plume fumaroles and occasional summit 

caldera phreatic eruptions

Qwws Shield lavas—Chiefly andesitic flows

Qwwv Valley-fill lavas—Lavas filled deeply incised glacial valleys cutting into the 

thick shield lavas (Qwws). A few far-reaching flows interbedded with the 

Copper River deposits (Qcr); chiefly andesite

Mount Drum volcano (Pleistocene, 0.6–0.2 Ma)—Constructed during andesitic 

cone (or shield) building and rhyolite-dacite ring dome emplacement cycles. A 

late (0.25 Ma) cataclysmic eruption destroyed top and south sides

Qwd Lava flows—Andesite and dacite flows; dikes

Qwdr Domes—Dacite and rhyolite domes; associated flows and dikes

Mount Sanford volcano (Pleistocene, 0.9–0.5 Ma)—Height and extensive ice 

cover limit understanding of volcanic structure. Edifice, apparently sourced 

from three major vents, is an intermingled complex of lava flows and domes, 

predominantly andesite, including a particularly extensive rhyolite flow

Qws Lava flows—Chiefly andesite and dacite

Qwsr Rhyolite dome and flow—Thick far-ranging flow (0.6 Ma) probably sourced 

from northeast flank dome

Capital Mountain volcano (Pleistocene, 1.0 Ma)—Small andesitic shield and 

summit caldera intruded at center by an andesite plug, focal point of a spectacular radial basaltic andesitic dike swarm

Qwc Shield and intracaldera lavas—Chiefly andesite

Qwcr Central andesite plug and dike swarm; rhyolite laccolith and associated dike—Plug represents final activity; dike originated from laccolith on 

shield’s southeast flank

Mount Jarvis volcanoes (Pleistocene, 1.7–1.0 Ma)—North-trending linear 

succession of centers including at least two summit calderas and eroded 

andesitic shields; satellite dacite domes and flows

Qwj Shield and intracaldera lavas—Extensive flat-lying andesitic flows 

Qwjd Domes—Final stage deposition at chain’s north end; dacite

Tanada Peak volcano (Pleistocene and Pliocene, 1.8–0.9 Ma)—Large shield 

and remnant summit caldera, stripped by erosion, remaindered to thick, 

massive intracaldera lavas as serrated topographic highs

QTwt Shield and intracaldera lavas—Andesite flows and local agglutinates
Other volcanic deposits

Volcaniclastic deposits (Pleistocene)

Qvd Volcanic debris flows—Chetaslina volcanic mass-flow deposit, probably 

sourced from Mount Drum, exposed along Chetaslina and Copper Rivers; 

Sanford volcanic debris flow exposed along Sanford and Copper Rivers. 

Large blocks of lava and varied debris

Qpf Pyroclastic flows—The extensive informally named Nadina hot avalanche 

deposit from Mount Drum’s cataclysmic eruption and a smaller pyroclastic 

flow (0.3 Ma), possibly derived during an explosive episode from Mount 

Drum, deposited at Chetaslina River’s two forks. Abundant bombs, scoria, 

pumice, and ash; lesser andesite and dacite blocks

Qbc Cinder cones, flows, and tuffs (Pleistocene)—Olivine basalt and basaltic 

andesite

Older volcanic and sedimentary rocks (Pleistocene, Pliocene, or Miocene)—

Boomerang (<1.0 Ma), Chetaslina (1.6–0.8 Ma), Skookum Creek (3.2–2.0 Ma)

Mount Blackburn (4.3–3.2 Ma), and other Early Quaternary to Late Tertiary 

volcanic centers. Sedimentary rocks crop out at base of Wrangell Lava

QTw Lava flows and sedimentary rocks—Flat-lying andesite and dacite 

lava flows; a Tertiary tillite and the fossil-rich conglomeratic sandstone 

Frederika Formation

QTwi Flows of the Ice Fields Plateau—Massive dacite and high-silica andesite 

lavas capping Ice Fields Plateau east of Nabesna Glacier

QTwr Domes and intrusive rocks—Chiefly dacite and rhyolite

Hypabyssal and plutonic rocks (Pleistocene, Pliocene, Miocene, or Oligocene)

QTwd Dikes—Chiefly andesite and dacite

Th Shallow plutons, small stocks, dikes, and sills—Andesite to dacite porphyry, diorite, and quartz diorite. K-Ar dates indicate ages that range from 

7.0 to 3.0 Ma, younger than the plutons (Tp) located on north side of 

Wrangell Mountains. Probably related to Wrangell volcanism, porphyry 

rocks may be hypabyssal equivalents of the older Wrangell lavas (QTw) and 

the Chisana Formation (Kc)

Tg Granodiorite—Plutonic phase of the Wrangell Lava exposed mainly at 

Hawkins Glacier head, marginal to Mount Blackburn volcano caldera

Oldest volcanic rocks (Miocene or Oligocene)—Sonya Creek (23–20 Ma) and 

other, unmapped, older Tertiary volcanic centers (26–23 Ma)

Tw Lava flows and lahars—Basaltic andesite, andesite, and dacite lava flows; 

andesitic lahar deposits

Twr Rhyolite flow—Obsidian-bearing lava within Sonya Creek caldera

Twd Domes—Dacite and rhyolite underlying the lava flows and lahar deposits 

(Tw) of Sonya Creek volcano

WINDY TERRANE

Sedimentary rocks

}c Conglomerate and sandstone (Early Cretaceous(?) and Late Jurassic(?) 

or older)—Pebble to boulder conglomerate and coarse-grained sandstone. 

May reflect the Nutzotin Mountains sequence (KJs) of Berg and others 

(1972) northern shore facies; hornfels alteration along southern contact of

the Snag pluton (Tsq)

Intrusive rocks

Tsq Snag pluton (Tertiary, 50 Ma)—Informally named body of leucocratic biotite 

quartz monzonite. K-Ar date indicates age of 50 Ma
Metamorphic rocks

Tc Metamorphic complex of Cottonwood Creek of Richter (1976) (Tertiary)—Banded granite and quartz diorite gneiss enclosed in schist and 

phyllite, most likely part of the Devonian metasedimentary (Dp) rocks. 

Greenschist to amphibolite metamorphism yields metamorphic age of 

20–17 Ma. Complex occurs within Denali Fault System between Nabesna

and Chisana Rivers

Metamorphic rocks of the Carden Hills (Permian(?), Pennsylvanian, Mississippian, and Devonian(?))

|v Metavolcanic rocks—Slightly porphyritic meta-andesite and metabasalt; 

greenschist-facies metamorphism

|vc Metavolcaniclastic rocks—Chiefly meta-sandstone, metatuff, and quartzite; 

greenschist-facies metamorphism

Dp Metasedimentary rocks (Devonian)—Mainly phyllite, also includes calcareous 

mica-schist, quartzite, metaconglomerate, and thin marble lenses. Greenschist-facies metamorphism. Contains poorly preserved Devonian fossils

Ultramafic and associated rocks

}|u Alpine-type ultramafic rocks and gabbro (Cretaceous(?), Jurassic(?), Triassic, Permian, and Pennsylvanian(?))—Serpentinized peridotite and dunite, 

locally containing chromitite, leucocratic gabbro, and hornblende gabbro

WRANGELLIA COMPOSITE TERRANE

PENINSULAR TERRANE

(West of Copper River)

Sedimentary, volcanic, and ultramafic rocks

Jnt Mafic and ultramafic rocks (Middle or Early Jurassic)—Gabbro, pyroxenite, 

peridotite and dunite. Includes the Nelchina River Gabbronorite, the Tonsina 

ultramafic, and a mafic sequence of Winkler and others (1980). K-Ar dates

indicate ages of 188–171

J^t Talkeetna Formation (Early Jurassic and Late Triassic(?))—Dominantly 

andesitic volcaniclastic rocks, products of Late Triassic and Early Jurassic 

oceanic volcanic arcs

WRANGELLIA TERRANE

(Eastern Alaska Range and Northern Wrangell Mountains)

Metamorphic rocks

P*dm Diorite complex, metamorphic part (Permian(?) and Pennsylvanian)—

Amphibolite-grade metamorphic rocks of mainly quartz-feldspar schist, 

biotite-hornblende gneiss, and syenite-monzonite gneiss. Jurassic K-Ar ages 

in probability reflect a metamorphic age. Together with associated late Paleozoic plutons (P*dp) construct part of the Skolai-Tetelna magmatic arc (P*t, 

P*s, and P*sc) and Pennsylvanian oceanic crust. Possibly correlative with 

the gabbro and orthogneiss (P*go) in southern Wrangell Mountains

Intrusive rocks

Tp Younger plutons (Tertiary)—Hornblende-feldspar and feldspar porphyry 

plutons; in part, related to Wrangell volcanism. K-Ar dates indicate ages of 

39–17 M
Kg Mid-Cretaceous plutons (Cretaceous)—Chiefly discordant plutons of granodiorite and quartz monzonite; also include quartz diorite, diorite, syenodiorite, 

and trondhjemite phases. K-Ar dates indicate ages of 117–105 Ma. Local

abundant xenoliths

P*dp Diorite complex, plutonic part (Permian(?) and Pennsylvanian)—Hornblende diorite grading into gneissic diorite. Together with associated metamorphics (P*dm), almost certainly represents the Skolai-Tetelna magmatic 

arc’s (P*t, P*s, and P*sc) roots. Possibly correlative with the gabbro and 

orthogneiss (*go) in southern Wrangell Mountains

*a Ahtell pluton (Pennsylvanian)—Quartz monzonite and granodiorite discordant zoned pluton. Together with the monzonite-granite complex (*m) 

in Saint Elias Mountains make part of the Skolai-Tetelna magmatic arc’s 

(P*t, P*s, and Phsc) core. K-Ar data indicates an age of 285 Ma

Sedimentary and volcanic rocks

Kun Nonmarine sedimentary rocks (Late Cretaceous)—Conglomerate, sandstone, 

siltstone, and mudstone locally containing abundant plant fossils

Kc Chisana Formation (Early Cretaceous)—Thick volcanic arc assemblage of 

marine and subaerial volcanic and volcaniclastic rocks. Younger part consists of andesite and basaltic andesite flows, and volcaniclastic rocks; older 

part consists of volcaniclastic rocks and locally fossil rich marine argillite 

and graywacke

KJs Nutzotin Mountains sequence of Berg and others (1972) (Early Cretaceous 

and Late Jurassic)—Argillite-graywacke graded beds and minor conglomerate, sandstone, and limestone; thick deep ocean trench fossil-poor 

marine flysch sequence bordering Wrangellia terrane

^l Triassic limestone (Late Triassic)—Locally fossil rich, thin-bedded limestone 

and interbedded argillite in partially starved marine basin; overlies shallow 

marine to intertidal fossil-poor cherty massive limestone

^n Nikolai Greenstone (Late and(or) Middle Triassic)—Widespread sequence of 

tholeiitic flood basalt flows, mainly subaerial and characteristically amygdaloidal; subordinate volcaniclastic interbeds and volcanic conglomerate basal 

sections. Metamorphosed to prehnite-pumpellyite facies although alteration 

rarely masks primary mineralogy and texture. Contains anomalously high 

amounts of copper

Mankomen Group (Early Permian and Pennsylvanian)—Marine sedimentary sequence consisting of the upper nonvolcanogenic Eagle Creek 

Formation (Pe and Pel) and the lower volcanogenic Slana Spur Formation 

(P*ss). Locally altered and metamorphosed. Correlates with the Skolai 

Group (P*s, Ph, Pl, and P*sc) in southern Wrangell Mountains

Pe Eagle Creek Formation (Early Permian)—Nonvolcanogenic argillite and 

siltstone deposited in a moderately deep quiet basin. Abundant fossils, 

cone-in-cone structures, and concretions. Intruded by locally abundant 

Triassic gabbroic inclusions (^n) and porphyry dikes and sills (Tp)

Pel Limestone of Eagle Creek Formation—Fossiliferous thin- to thick-bedded 

limestone

P*ss Slana Spur Formation (Early Permian and Pennsylvanian)—Fossil-rich 

volcanic sandstone, siltstone, conglomerate, and impure bioclastic limestone; shed off the Tetelna volcanic arc (P*t)

P*t Tetelna Volcanics (Early Permian and Pennsylvanian)—Subaerial and submarine basaltic to dacite lava, lahar flows, tuff deposits, and fine-grained 

volcaniclastic rocks. Extensive late Paleozoic magmatic arc vestiges form 

Wrangellia terrane’s basement in northern Wrangell Mountains and eastern 
Alaska Range. Correlates to the Skolai Group’s (P*s) Station Creek Formation (P*sc) in southern Wrangell Mountains

WRANGELLIA TERRANE

(Southern Wrangell Mountains and Saint Elias Mountains)

Sedimentary and volcanic rocks

Ku Marine sedimentary rocks (Early and Late Cretaceous)—Sandstone and 

siltstone deposited at shallow to moderate depths; locally abundant marine 

fossils. Includes the MacColl Ridge, Chititu, Schulze, and Moonshine Creek 

Formations

Kl Shallow marine sedimentary rocks (Early Cretaceous)—Conglomerate, 

sandstone, siltstone, and clastic sandy limestone deposited under nearshore, 

high-energy, transgressive marine conditions; locally includes concretions 

and abundant fossils. Includes the Kennicott, Kuskulana Pass, and Berg 

Creek Formations

Js Sedimentary rocks (Late, Middle, or Early Jurassic)—Chiefly spiculite, 

graywacke, mudstone, and conglomerate deposited in a shallow-marine 

and nearshore littoral setting. Includes the fossil-rich Lubbe Creek, Nizina 

Mountain, and Root Glacier Formations

Jk Kotsina Conglomerate—Conglomerate and minor sandstone deposited under 

rapid local marine circumstances during orogenesis. Fossils absent

J^m McCarthy Formation (Early Jurassic and Late Triassic)—Spiculite, impure 

chert and limestone, and shale deposited in a starved marine basin environment. Fossils locally abundant

^cn Chitistone and Nizina Limestones (Late Triassic)—Chiefly limestone and 

dolomite; minor chert and marble; locally fossil rich. The upper Chitistone and cherty Nizina, deposited in a shallow to moderately deep marine 

neritic environment, transition into an intertidal-supratidal setting with 

local sabkha facies full of algal-mat chips, stromatolites, and evaporate 

relics typical of the dolostone-rich lower Chitistone rocks

^n Nikolai Greenstone (Late and(or) Middle Triassic)—Widespread sequence 

of tholeiitic flood basalt flows, mainly subaerial and characteristically 

amygdaloidal, include subordinate volcaniclastic interbeds and volcanic 

conglomerate basal sections. Metamorphosed to prehnite-pumpellyite 

facies although alteration rarely masks primary mineralogy and texture. 

Contains anomalously high amounts of copper

P*s Skolai Group, undivided (Early Permian and Pennsylvanian)—Lower late 

Paleozoic magmatic arc and associated upper sedimentary rocks. Equivalent 

to the Mankomen Group (Pe, Pel, and P*ss) and the Tetelna Volcanics 

(P*t) in northern Wrangell Mountains and eastern Alaska Range

Ph Hasen Creek Formation (Early Permian)—Fossil-rich marine argillite, 

shale, and sandstone; nonvolcanic origin

Pl Limestone of Hasen Creek Formation—Fossil-rich, lenticular, marine 

limestone; partially equivalent to the Strelna metamorphic marble of Plafker 

and others (1989) (P*m

P*sc Station Creek Formation (Early Permian and Pennsylvanian)—Magmatic 

arc consists of a younger volcaniclastic member and an older andesitic and 

basaltic lava flow member, both of submarine origin; locally metamorphosed to greenschist-facies south of Chitina Fault

Intrusive rocks

Jc Chitina Valley batholith (Late Jurassic)—Compositionally diverse quartz 

monzodiorite, ranging from granite to diorite, generally foliated and locally 
1

gneissic particularly within plutons enclosed by the Strelna Metamorphics 

of Plafker and others (1989) (P*sm). K-Ar dates indicate plutonic ages of

157–138 Ma, foliated phase ages are as young as 122 Ma; synchronous wi

Late Jurassic major regional orogeny perhaps related to subduction along 

Border Ranges Fault

*m Monzonite-granite complex (Pennsylvanian)—Large composite granite and 

quartz monzonite pluton containing lesser monzonite, syenite, and gabbro 

emplaced between Wrangellia and Alexander(?) terranes. K-Ar dates 

indicate ages of 297–295 Ma. Correlates with the Ahtell pluton (*a) in 

northern Wrangell Mountains to construct the Tetelna-Skolai magmatic 

arc’s (P*t, P*s, and P*sc) core

*go Gabbro and orthogneiss (Pennsylvanian)—Interlayered hornblende pyroxene 

gabbro and monzonitic gneiss; overlain by the Skolai Group (P*s, Ph, Pl, 

and P*sc) and their metamorphosed equivalent, the Strelna Metamorphics 

of Plafker and others (1989) (Phsm). Represents, in part, Pennsylvanian

oceanic crust correlative with the diorite complex (P*dm and P*dp) in 

northern Wrangell Mountains and eastern Alaskan Range

Metamorphic rocks

P*sm Strelna Metamorphics of Plafker and others (1989) (Jurassic(?), Triassic(?), 

Permian, Early Pennsylvanian, and Late Mississippian(?))—Dominantly calcareous metasedimentary rocks, schist, phyllite, amphibolite, 

and marble; lesser quartzite, meta-andesite, and metabasalt in thin to thick 

thrust sheets containing local pods of the tectonically emplaced ultramafic 

rock and marble (P*m); overlying the gabbro and orthogneiss (*go). 

Includes the Jurassic Uranatina Metaplutonic Complex and the Dadina 

Schist of Carboniferous and possibly older(?) age exposed near Mount 

Drum. Metamorphic grade increases closer to the Chitina Valley batholith 

(Jc) and might represent metamorphosed roots of the Skolai–Tetelna magmatic arc (P*t, P*s, and P*sc)

P*m Marble—Regionally metamorphosed with poorly preserved and locally 

placed Permian and Early Pennsylvanian fossils. Partially equivalent to the 

Permian limestone of the Hasen Creek Formation (Pl)

ALEXANDER(?) TERRANE

(Saint Elias Mountains)

Metamorphic rocks

|k Kaskawulsh Group of Kindle (1953) (Pennsylvanian, Mississippian, Devonian(?), and older)—A metamorphosed marine sequence of marble, schist, 

and phyllite; minor meta-tuff, flows, breccia, and meta-conglomerate; 

probably oceanic crustal progression with carbonate reefs. Poorly preserved 

Ordovician, Devonian, and possible Mississippian and Pennsylvanian fossils 

present. Metamorphosed to upper greenschist-facies and locally intensely 

folded. Coextensive with widely occurring rocks within neighboring Yukon 

Territory, Canada; potentially representing westernmost known extent of 

Alexander(?) terrane

SOUTHERN MARGIN COMPOSITE TERRANE

CHUGACH TERRANE

Sedimentary, volcanic, and metamorphic rocks

Valdez Group (Late Cretaceous)—Mainly mudstone and graywacke turbidite beds, 

carbonaceous phyllite, minor mafic tuff and breccia in a thick regionally 
extensive belt of accreted flyschoid deep marine rocks. Metamorphic grade 

increases southward from lower greenschist-facies to amphibolite-facies

Kv Greenschist-facies flysch—Flysch metamorphosed to lower greenschist-facies

Kvv Metamorphosed basalt and tuff—Tholeiitic metabasalt and basaltic metatuff, local pillow lava and pillow breccia, gabbroic dikes and sills

Kvm Amphibolite-facies flysch—Flysch metamorphosed to amphibolite-facies 

schist

Kvg Gneiss and schist—Gneiss, banded and migmatite. Includes the amphibolitefacies schist of Mount Augusta of Plafker (written commun., 2000)

KJm Mélange units (mid-Cretaceous, Jurassic, and Late Triassic(?)—Tholeiitic 

pillowed basalt, chert, tuff, greywacke, argillite, and phyllite-greenstone 

deposited along a convergent plate margin as early as Late Triassic continuously into middle Cretaceous. Includes the McHugh Complex, a structurally complex and chaotic assemblage of oceanic rocks containing abundant 

slightly deformed radiolarian chert; and a mélange-like unit between the 

McHugh Complex and the Valdez Group (Kv)

Jlc Schist of Liberty Creek of Winkler and others (1981) (Jurassic(?))—Basalt 

flows, breccia, and tuff; regionally metamorphosed greenschist- and blueschist-facies Middle Jurassic or older oceanic assemblage protolith

Intrusive rocks

Tgp Granitic plutons (Eocene, 50 Ma)—Granite, granodiorite, and diorite intruding 

Chugach and Prince William terranes; intermediate composition Eocene age 

dikes not shown on map

PRINCE WILLIAM TERRANE

Sedimentary and volcanic rocks

Orca Group (early Eocene and late Paleocene)—Weakly metamorphosed 

flysch and basalt thick submarine fan complex

Tos Turbidites—Mudstone to sandstone, locally fossil rich, submarine gravity flows

Tov Basalt—Mainly tabular bodies of pillowed, massive, and columnar jointed 

tholeiitic basalt lava flows; locally interbedded minor mudstone and siltstone

Intrusive rocks

Tgp Granitic plutons (Eocene, 50 Ma)—Granite, granodiorite, and diorite intruding 

Chugach and Prince William terranes; intermediate composition Eocene age 

dikes not shown on map

YAKUTAT TERRANE

Sedimentary, volcanic, and metamorphic rocks

QTy Yakataga Formation (Holocene(?), Pleistocene, Pliocene, and Miocene)—

Mudstone, siltstone, sandstone, and diamictite in a diverse marine and 

glacio-marine clastic continental shelf deposit. Abundant mega- and microfauna

Tm Volcanic and hypabyssal rocks (Miocene and Oligocene)—Basalt to andesitic 

plugs, dikes, and flows

Tps Poul Creek Formation (early Miocene(?), Oligocene, and late Eocene(?))—

Concretionary marine siltstone, claystone, sandstone, and conglomerate, 

minor basaltic tuff, and locally glauconitic. Includes part of the clastic Redwood Formation and, as mapped, forms part of Robinson Mountains north 

of Cape Yakataga
1

Tt Tokun Formation (Eocene)—Shallow marine concretionary siltstone and 

minor sandstone

Tk Kulthieth Formation (Eocene and early Paleocene(?))—Interbedded nonmarine carbonaceous sandstone, siltstone, shale, and minor coal; sparse warmwater marine molluscan megafauna and locally abundant subtropical plant 

fossils. Includes small occurrences of the siltstone-rich Stillwater Formation 

east of Steller Glacier, the siltstone of Oily Lake of Plafker (1987), and the

basalt of Hubbs Creek of Plafker and others (1987) found in Samovar Hills,

a Malaspina Glacier nunatak

Kyn Schist of Nunatak Fiord (Cretaceous)—Complexly deformed interbedded mudstone and sandstone, minor volcaniclastic rocks and conglomerate; 

metamorphosed to greenschist- and epidote-amphibolite facies. Crops up 

between Boundary and Fairweather Fault Systems and intruded extensively 

by the Tertiary granitic plutons (Tgp) (Plafker, written commun., 2000)

Yakutat Group (Cretaceous and Jurassic(?))—Complexly deformed flysch 

and mélange locally recrystallized to greenschist

Kyf Flysch—Graywacke, siltstone, and argillite

Kym Mélange—Discrete blocks of greenstone, limestone, marble, graywacke, 

chert, conglomerate, and plutonic rocks, up to several kilometers in greatest 

dimension, in a sheared matrix of mudstone

Intrusive rocks

Td Rhyolite porphyry and granite (Pliocene(?) or Miocene(?))—Discordant hypabyssal plutons and dikes exposed between Mount Augusta and Mount Cook

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