Prepared in cooperation with the National Park Service

Geologic Map of the Valdez D-1 and D-2 Quadrangles 

(Mount Wrangell Volcano), Alaska

By D.H. Richter, R.G. McGimsey, K.A. Labay, M.A. Lanphere, R.B. Moore, C.J. Nye, D.S. Rosenkrans, 

and G.R. Winkler

Pamphlet to accompany

Scientific Investigations Map 3351

2016

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit

http://www.usgs.gov/ or call 1–888–ASK–USGS (1–888–275–8747).

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod/.

To order USGS information products, visit http://store.usgs.gov/.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply

endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also may

contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items

must be secured from the copyright owner.

Suggested citation:

Richter, D.H., McGimsey, R.G., Labay, K.A., Lanphere, M.A., Moore, R.B., Nye, C.J., Rosenkrans, D.S., and 

Winkler, G.R., 2016, Geologic map of the Valdez D-1 and D-2 quadrangles (Mount Wrangell Volcano), Alaska: U.S. 

Geological Survey Scientific Investigations Map 3351, 20 p., scale 1:63,360, http://dx.doi.org/10.3133/sim3351.

ISSN 2329-132X (online)
iii

Contents

Geologic Note ................................................................................................................................................................1

Acknowledgments..........................................................................................................................................................2

Description of Map Units ................................................................................................................................................3

Surficial Deposits........................................................................................................................................................3

Alluvial Deposits .....................................................................................................................................................3

Colluvial Deposits ...................................................................................................................................................3

Glacial Deposits......................................................................................................................................................3

Glaciolacustrine Deposits .......................................................................................................................................4

Quaternary Volcanic and Sedimentary Rocks ............................................................................................................4

Mount Wrangell Volcano.........................................................................................................................................4

Mount Drum Volcano ..............................................................................................................................................7

Volcaniclastic Deposits ...........................................................................................................................................7

Basaltic Andesite–Dacite Center.............................................................................................................................8

Shallow Intrusive Rocks..........................................................................................................................................9

Chetaslina Lavas ....................................................................................................................................................9

Sedimentary Rocks...............................................................................................................................................10

Mesozoic and Paleozoic Rocks................................................................................................................................11

References Cited .........................................................................................................................................................12

Figures

 1. Generalized map showing present extent of Mount Wrangell lavas (red), Valdez D-1 and D-2 

quadrangles, and sample locations (dots) outside Valdez D-1 and D-2 map area. All other rocks are 

tan, surficial deposits are yellow, ice is white, and rivers are blue ............................................................ 14

 2. Total alkalis (Na2O+K2O) versus silica contacts for volcanic rocks from the Valdez D-1 and D-2 

quadrangles, Alaska ................................................................................................................................. 15

Tables

 1. Chemical analyses of volcanic rocks from the Valdez D-1 and D-2 quadrangles, Alaska......................... 16

 2. Radiometric ages from map units in the Valdez D-I and D-2 quadrangles, Alaska................................... 19

Map Sheet

 1. Geologic Map of the Valdez D-1 and D-2 Quadrangles (Mount Wrangell Volcano), Alaska

By D.H. Richter, R.G. McGimsey, K.A. Labay, M.A. Lanphere, R.B. Moore, C.J. Nye, D.S. 

Rosenkrans, and G.R. Winkler
1

Geologic Map of the Valdez D-1 and D-2 Quadrangles 

(Mount Wrangell Volcano), Alaska 

By D.H. Richter, R.G. McGimsey, K.A. Labay, M.A. Lanphere, R.B. Moore, C.J. Nye, D.S. Rosenkrans, 

and G.R. Winkler

Geologic Note

Mount Wrangell (elev. 4,317 m) is the youngest and only active volcano in the Oligocene to 

Holocene-aged Wrangell volcanic field that extends from beyond the Alaska-Yukon border northwest 

through the Wrangell Mountains to the Copper River Basin. The volcano is a very large (900 km3

; Nye, 

1983) broad shield containing an ice-filled, nonexplosive, collapse caldera measuring 3.2 by 5.6 

kilometers. Three known craters, the West, North, and East occur along the north and west margins of 

the caldera; the caldera is open to the southeast. The volcano is best exposed on its southwest flank (this 

map area) where a number of deep glaciated canyons cut through hundreds of meters of shield lava 

flows creating routes for younger, valley-filling lava flows. The shield extends north into the Gulkana 

A-1 quadrangle (Richter and others, 1994), northeast into the Nabesna A-6 quadrangle (Richter and 

others, 1997), and east into the McCarthy quadrangle (MacKevett, 1978) where it is almost entirely 

covered by ice. The present extent of the Mount Wrangell shield showing the entire caldera and 

locations of the three summit craters is depicted in figure 1.

Mount Wrangell was built rapidly beginning about 650 ka by the outpourings of hundreds of 

voluminous lava flows from a vent, or vents, apparently in the present summit area. By 200 ka to 300 

ka, activity waned and only an occasional lava flow coursed down the glacially carved valleys radiating 

from the summit or flowed over the upper summit area above the heads of the glacial valleys. The 

youngest dated valley-fill lava flow is approximately 25,000 years old; one or two undated flows may 

be younger. 

In historical times there have been several reports of lava flows issuing from the summit area. 

The most reliable and convincing of these were two independent observations (Powell, 1900; Rice, 

1900) from Copper Center, Alaska on September 3, 1899 that described great earth movements (the 

1899 Yakutat Bay earthquake; Tarr and Martin, 1912) followed by an eruption at Mount Wrangell’s 

summit, consisting of vigorous ash emission and flowing lava on the volcano’s northwest flank. This 

eruptive activity apparently continued for several years after the earthquake, as a photo taken around 

1901–02 by Mendenhall and Schrader (1903) shows a large part of Mount Wrangell’s summit blanketed 

by ash. During this study, no evidence of young lava flows in the region were found, although it is very 

possible that a small-volume flow could be entirely hidden by snow and ice in the 100 years since the 

event. However, abundant juvenile andesitic pumice (no. 73 on map) was found on the upper Chetaslina 

Glacier, strongly supporting a very young pyroclastic eruption. 

In addition to the 1899–1902 eruptions there have been accounts of strong ash-producing 

activity on at least four different occasions (Clarke and others, 1989): 1912, July 3, 1921, April 6, 1930, 
2

and February 20, 1982. Of these, the 1921 activity was the most spectacular, and possibly erupted from 

the northeast side of the summit caldera (Clarke and others, 1989).

Present activity is limited to fumaroles in North and West Crater at the summit, at the summit 

ridge near East Crater, and at two localities at an elevation of 3,657 m on the southwest flank. The 

summit fumaroles frequently give rise to visible steam plumes (Neal and others, 2014), and occasionally 

sporadic explosive phreatic activity in North and West Crater will put a thin dusting of ash on the 

summit ice. The summit area and craters are described by Benson and Motyka (1979) and Benson and 

Follett (1986).

This study was directed toward Mount Wrangell volcano and the older Wrangell volcanic field 

rocks that underlie the volcano. These older lavas include the Chetaslina lavas (867 ka–1,650 ka) and a 

basaltic andesite–dacite center (1,590 ka–1,640 ka) whose source areas are not well defined. Older 

Paleozoic and Mesozoic sedimentary, igneous, and metamorphic rocks of the Wrangellia terrane 

underlie the entire Wrangell volcanic field. These old basement rocks, as shown on this map, are taken 

directly from Winkler and others (1995); further information on these rocks is available from Winkler 

and others (1981) and Richter and others (2006).

Radiometric ages listed under map letters A, G, H, I, R, X, and Y (table 2) have been previously 

reported (Nye, 1983); all other ages are new. The sample at map letter N (italicized) is from the Long 

Valley flow in the contiguous Valdez C-1 quadrangle.

Acknowledgments

This is the final geologic publication of Donald H. Richter, who passed away in 2004 while

finalizing this map. Don was our close friend and esteemed colleague, and he is sorely missed. The 

fieldwork on this mapping project was conducted in 1999 and 2000 with much of the background 

understanding of the Wrangell volcanic field based on Don’s many years working in the area. We are 

grateful to Christina Neal and Jim Ratté for their technical reviews of the map, and to Scott Starratt for 

his review of the geologic names. Carolyn Donlin edited the map. Jackie McIntyre contributed to the 

initial digital cartography. We extend our sincere appreciation to the staff of the Wrangell-Saint Elias 

National Park and Preserve, as well as to John Staples and Patty Ryan, owners and proprietors of the 

Golden Spruce Cabins who, in addition to rooms and meals, provided logistical support for the 

helicopter and fuel staging. Cindi Preller assisted Don during the final weeks of his work on the map 

and transferred all the materials to the coauthors for completion. Additional colleagues who worked in 

the area during the project are Chris Waythomas and Kristi Wallace (Chetaslina debris flow), and Jon 

Hagstrum (paleomagnetic analysis). Andy Calvert provided an 40Ar/39Ar age date, and some radiometric 

ages were determined by D.L. Turner and Nora Shew.
3

DESCRIPTION OF MAP UNITS

SURFICIAL DEPOSITS

ALLUVIAL DEPOSITS

Qa Alluvium in streams (Holocene and Pleistocene)—Includes alluvium in active 

flood plains and in principal terraces of major, and some minor, streams.

Primarily stratified silt, sand, gravel, and boulders

Qaf Alluvium in fans (Holocene and Pleistocene)—Mainly large, broad, generally 

active fans and cones on mountain slopes predominantly along major streams.

Primarily sand, gravel, and boulders

Qoa Older alluvium (Pleistocene)—Thick inactive fans that have been dissected by 

modern drainages near the present toes of the Chetaslina Glacier and the East 

Fork of the Chetaslina Glacier. The deposits are exceptionally well stratified 

southeast of the toe of the Chetaslina Glacier. Chetaslina lavas (unit Qcl) are 

exposed in the unit and it is not clear whether the lavas are interbedded in the 

alluvium or overlain by alluvium. Primarily sand, gravel, and boulders; may 

include some diamicton. Maximum thickness about 150 m

COLLUVIAL DEPOSITS

Qc Colluvium, undivided (Holocene and Pleistocene)—Primarily talus but includes 

deposits of small landslides, rock glaciers, and other mass-wasting processes. 

Includes a large proportion of alluvium in small fans and cones and reworked 

glacial deposits. Shown mainly where deposits cover pre-Cenozoic bedrock 

and Quaternary volcanic rocks, and locally where deposits mantle steep 

slopes of older glacial deposits (unit Qog). Not shown, but present, on the 

steep valley walls of the Chetaslina, East Fork of the Chetaslina, and 

Cheshnina Rivers where the rivers have incised the glaciolacustrine deposits 

of the Copper River Basin (unit Qlg). Primarily poorly sorted silt, sand, 

gravel, and boulders

GLACIAL DEPOSITS

Qr Rock glacier deposits (Holocene)—Includes deposits in active rock glaciers that 

have well-defined lobate and tongue-shaped forms, small coalescing rock 

glaciers that form linear ridges along bases of steep slopes, and largely 

inactive rock glaciers with smooth surfaces. Primarily angular blocks and 

diamicton

Qag Drift of Alaskan glaciation (Holocene)—Includes end and lateral moraines of the 

younger and older phases of Alaskan glaciation, deposited after recession of 

existing glaciers. Diamicton, local gravel, and sand

Qyg Drift of younger (Wisconsin) glaciation (Pleistocene)—Well-defined lateral 

moraines high on the valley walls of the Dadina, Chetaslina, and East Fork of 

the Chetaslina Rivers. Diamicton

Qog Drift of older (Wisconsin and older?) glaciation (Pleistocene)—Ground moraine 

extensively modified by alluvial and colluvial processes. Includes at least two 
4

interbedded lava flows from Mount Wrangell (unit Qwv). Diamicton; locally 

alluvial sand, gravel, and boulders

GLACIOLACUSTRINE DEPOSITS

Qlg Deposits of the Copper River basin, undivided (Pleistocene)—Primarily diamicton 

interbedded with stratified lacustrine sediments of glacial Lake Atna 

(Ferrians, 1989), but unit includes older glacial, lacustrine, and fluvial 

deposits that underlie the late Pleistocene glacial lake. The diamicton 

interbedded in the lake sediments ranges from nonsorted till to deposits of 

poorly sorted material that show graded bedding. The lake sediments, 

consisting of sand, silt, and clay, locally contain ice-rafted dropstones 

(Ferrians, 1989). The contact between these mixed glacial and lacustrine 

deposits and upland drift (unit Qog) and Pleistocene volcanic and older 

bedrock is arbitrarily shown as a long dashed line at an elevation of about 

2,450 ft above sea level, the approximate elevation of the prominent upper 

strand line of glacial Lake Atna in the eastern part of the Copper River Basin 

(Ferrians, 1989). Interbedded within the unit in the southwest part of the map 

area are the Chetaslina debris flow (unit Qcf), a pyroclastic flow (unit Qpf, 

342 ka, map letter BB), and at least one lava flow from Mount Wrangell (unit 

Qwv, 430 ka, map letter H). An overlying subaerial Mount Wrangell lava 

flow (unit Qwv, 76 ka, map letter L) suggests that glacial Lake Atna had 

emptied, or was very shallow, by 76 ka. Diamicton, gravel, sand, silt, and clay

QUATERNARY VOLCANIC AND SEDIMENTARY ROCKS

MOUNT WRANGELL VOLCANO

Mount Wrangell volcano (Holocene and Pleistocene, 0.65 Ma and younger)—Mount 

Wrangell is a large broad shield whose summit area contains a nonexplosive, ice-filled caldera. 

The lavas of the Mount Wrangell shield show a remarkable relatively uniform major element 

chemical composition (fig. 2) over a time span of more than 600,000 years. With only minor 

exceptions, the lavas are highly porphyritic, two-pyroxene, high-silica andesites whose silica 

content ranges from 60.0 to 63.3 percent. Mount Wrangell shield may be unique having been 

built by these relatively viscous flows of andesite.

Qwc Pyroclastic deposits of the Mount Wrangell West Crater (Holocene)—No attempt 

was made during this study to examine the fragmental and (or) pyroclastic 

deposits associated with the West Crater. Samples collected from the summit 

craters by R.B. Forbes, G.B. Wharton, and C.S. Benson of the University of

Alaska, Fairbanks, during 1961–67 are altered andesite flows, breccias, and 

tuffs. One of these samples from the East Crater (4 km northeast of the map 

area in the Gulkana A-1 quadrangle, see fig. 1) is described by Furst (1968) as 

an altered, olivine-bearing, two-pyroxene andesite

Qwv Mount Wrangell valley-fill and basin lavas (Holocene and Pleistocene)—

Moderately to highly porphyritic, two-pyroxene high-silica andesite flows 

mineralogically and chemically (60.9–63.6 percent SiO2, map nos. 29–49 

[Note that nos. 31 and 32 are from the contiguous Valdez C-1 quadrangle]) 

identical to Mount Wrangell shield lavas. Flows traveled down the deeply 
5

incised glacial valleys that radiate from the summit ice field on the shield and 

out into the Copper River Basin where they are interbedded with basin 

sediments (unit Qlg). Two flows range from about 6 m to more than 100 m 

thick (116 ka and 378 ka, map letter N and Q) that apparently built up behind 

ice dams. Well-developed, vertical, and highly contorted columnar joints are 

common in both; the degree of contortion suggests ice contact conditions. Ice 

contacts are also indicated by glassy hyaloclastite breccias at the base and 

margins of some flows. Two of the flows (81 ka and 105 ka, map letters M 

and K) in the East Fork of the Chetaslina River show inflated pahoehoe 

surfaces that are mantled by thin scattered glacial deposits.

At least 14 separate flows have been recognized in the East Fork of 

the Chetaslina River valley and at least four separate flows in the Cheshnina 

River valley. Where a contact is discernible a long dashed line represents the 

contact between individual flows. Whole-rock K-Ar ages of the flows (map 

letters G–Q; except for N, which is on Valdez C-1 quadrangle) range from 25 

ka to 430 ka. Age results for these flows are shown as a boxed bold number.

Two disparate dates (270 ka and 378 ka, samples 79cnc-1 and 00MC-2) were 

obtained on what was thought to be a single flow. Either the dates indicate 

two separate flows or, if a single flow, a measure of the reliability of the K-Ar 

method for young andesitic lavas. The longest (50 km) and very likely the 

largest of the late valley flows (116 ka) from Mount Wrangell, which is 

referred to as the Long Glacier flow, came down the Cheshnina River valley, 

spread out and thickened to more than 100 m probably behind an ice dam in 

the Copper River Basin. Most of this flow, including the terminus, is in the 

adjacent Valdez C-1 and C-2 quadrangles, where the age date (letter N, table 

2) and chemistry (nos. 31 and 32, table 1) samples were collected (see fig. 1)

Qwu Mount Wrangell lavas, undivided (Holocene and Pleistocene)—Restricted to 

exposures in unvisited nunataks on the upper slopes of Mount Wrangell above 

the heads of glacial valleys. Ages possibly as young as a few thousand years

Qw Lava flows of the Mount Wrangell shield (Pleistocene)—Medium to dark gray, 

moderately to highly porphyritic, two-pyroxene, high-silica andesite flows 

containing phenocrysts of plagioclase (10–50 percent, as much as 6 mm), 

orthopyroxene (1–6 percent, as much as 4 mm), clinopyroxene (1–7 percent, 

as much as 3 mm), locally opaque minerals, and an occasional trace of olivine 

in a glassy, cryptocrystalline, or microcrystalline groundmass. Plagioclase 

microlites are common in the more crystalline groundmasses. Plagioclase 

phenocrysts typically occur as single zoned crystals that are euhedral to 

slightly rounded. Inclusions are common to abundant, especially in interior 

zones; outermost zones are generally clear. Orthopyroxene tends to be more 

abundant than clinopyroxene and both, together with plagioclase, are 

relatively common in crystal clots as much as 6 mm in diameter. SiO2 content 

is restricted to a relatively narrow range of 60.0 to 62.5 percent (map nos. 1–

23). Whole-rock K-Ar ages range from 90 to 662 ka (map letters A–F, CC).

Individual flows range from 3 to more than 20 m thick and generally show 

fragmented and scoriaceous tops and bottoms. Crudely developed columnar 

joints are locally common. No volcaniclastic rocks were observed. Maximum 
6

total thickness about 750 m.

In the rugged isolated area covered by Mount Wrangell lavas between 

the East Fork of the Chetaslina and the main Chetaslina Rivers the flows are 

predominantly porphyritic high-silica andesites typical of other Mount 

Wrangell lavas. Locally, however, at the base of the unit, but not 

differentiated on the geologic map, are aphanitic to microporphyritic and 

slightly porphyritic flows not observed elsewhere on the Mount Wrangell 

shield. The microporphyritic flows contain 1–5 percent microphenocrysts (<1 

mm) of plagioclase, traces of both orthopyroxene and clinopyroxene, and an 

occasional highly altered crystal of hornblende in a glassy to cryptocrystalline 

groundmass. SiO2 content ranges from 62.2 to 63.3 percent (map nos. 24–28), 

slightly higher than the stratigraphically higher and typical porphyritic flows 

elsewhere on the shield. The one slightly porphyritic flow observed contains 

phenocrysts of plagioclase (1–3 percent, as much as 2 mm) and olivine (1–4

percent, as much as 3 mm) in a groundmass of aligned plagioclase microlites.

The whole-rock age of this flow is 662 ka (map letter C) suggesting that these 

aphanitic to microporphyritic and slightly porphyritic flows represent some of 

the initial lavas of Mount Wrangell. Possibly some of these flows may also be 

products of a small eruptive center associated with the nearby “Tusk” plug 

(unit Qwp).

A series of three or four very thick (locally >30 m) flows capping the 

high plateau between the Cheshnina River and Long Glacier are physically 

distinct and younger (90 ka, map letter E) than most of the observed Mount 

Wrangell shield lavas. They are differentiated on the geologic map by a 

dashed line. The flows contain phenocrysts of plagioclase, orthopyroxene, 

and clinopyroxene and contain 62.0 percent SiO2 (map no. 6), all features 

similar to other shield lavas. However, the flows are much thicker and lighter 

in color (medium gray) than most shield lavas. Individual flows show welldeveloped ramp structures and the group unconformably overlies thinner and 

older Mount Wrangell shield lavas.

As shown, unit Qw may include younger valley-fill lavas (unit Qwv) 

low in the valley walls of the East Fork of the Chetaslina River from the toe 

of the East Fork glacier downstream a distance of 5 to 6.5 km. Hyaloclastite 

deposits are locally exposed in a few side drainages in this area but exposures 

are poor owing to mantling by colluvium and they are not differentiated on 

the map

Qwp Andesite plug of Mount Wrangell (Pleistocene)—A sharp andesite spire, about 40 

meters high, referred to as “Tusk”, intrudes lavas of Mount Wrangell shield 

(unit Qw) near the terminus of the Chetaslina Glacier. The rock is a medium 

gray, plagioclase-rich, porphyritic andesite containing phenocrysts of fresh, 

euhedral plagioclase (60–80 percent, as much as 3 mm), clinopyroxene (4–6

percent, as much as 3 mm), and orthopyroxene (3–5 percent, as much as 2 

mm) in a cryptocrystalline groundmass. SiO2 content is 62.4 percent (map no. 

71). The plug may be a source of a few nearby aphanitic to microporphyritic 

flows (not identified on map) exposed at base of enclosing lavas of Mount 

Wrangell shield. Whole-rock K-Ar age is 529 ka (map letter S)
7

Qwe Early lava flows of Mount Wrangell (Pleistocene)—Exposed at the base of a 750-

m section of lava flows of Mount Wrangell shield, north of the Chetaslina 

Glacier, and in three isolated localities as single flows within Pleistocene 

glacial deposits (unit Qog). The flows north of the Chetaslina Glacier, which 

form a distinct unit as much as 150 m thick, are porphyritic, olivine-bearing, 

two-pyroxene andesites that show magma mixing features and contain 54.3 to 

58.5 percent SiO2 (Nye, 1983). The isolated flows are also olivine-bearing 

two-pyroxene porphyritic to seriate andesites; one flow contains 57.4 percent

SiO2 (map no. 50). A flow low in the section north of the Chetaslina Glacier 

yielded a K-Ar age of 690 ka (map letter R)

MOUNT DRUM VOLCANO

Qda Nadina volcanic avalanche, landslide, and glacial deposits, undivided 

(Pleistocene)—Variegated, crudely stratified and poorly sorted juvenile 

bombs, pumice, ash and blocks of andesite and dacite that resulted from 

paroxysmal explosive activity within the central vent area of Mount Drum 

(Richter and others, 1979). Deposits are locally covered by, and mixed with, 

glacial drift

Qdl Andesite flows (Pleistocene)—Medium to dark gray, porphyritic, olivine-bearing 

andesite lava flows containing phenocrysts of plagioclase (10–15 percent, as 

much as 3 mm), fresh olivine (4–6 percent, as much as 3 mm), and 

orthopyroxene (2–3 percent, as much as 1 mm) in a cryptocrystalline 

groundmass. SiO2 content is 60.8 percent (map no. 72). In adjacent northern 

quadrangle (Gulkana A-2), some flows also contain clinopyroxene and 

hornblende (Richter and others, 1979). Flows are thick (>10 m) and may have 

a source in the vicinity of the Snider Peak dome on Mount Drum, 8 km to the 

north 

VOLCANICLASTIC DEPOSITS

Qcf Chetaslina volcanic debris flow (Pleistocene)—Multi-colored, voluminous (7–12 

km3) debris avalanche deposit containing megablocks, as much as 90 m in 

maximum dimension, of both porphyritic and aphanitic andesite lava, 

hydrothermally altered lava, volcanic breccia, pyroclastic flow deposits, 

lacustrine sediments, and glacial deposits. Unit underlies a 270-ka Wrangell 

lava flow (map letter G, unit Qwv) and probably is younger than a 342-ka 

pyroclastic flow (map letter BB, unit Qpf) in the valley of the East Fork of the 

Chetaslina River. Although the debris flow is not in contact with the 

pyroclastic flow, bombs apparently from the pyroclastic flow occur in the 

debris flow. The maximum thickness is about 100 m. The deposit’s source is 

equivocal: originally thought to be related to a summit collapse of Mount 

Wrangell (Yehle and Nichols, 1980), later Richter and others (1995) 

suggested that the deposit was a result of the cataclysmic eruption that 

destroyed the top of Mount Drum. More recently, Waythomas and Wallace 

(2002) concluded that the deposit is associated with a sector collapse of 

Mount Wrangell’s flank in the area of the Chetaslina lavas (unit Qcl).

However, the age of lava flows that once covered this potential source area 
8

(map letter C) casts doubt on that interpretation

Qpf Pyroclastic flow (Pleistocene)—Pale to medium yellowish brown pyroclastic flow 

deposit containing abundant bombs, scoria, and pumice as much as 15 cm in 

diameter. Analyses of five scoria and pumice clasts suggest a bimodal 

andesite-dacite distribution (60.0–61.4 percent SiO2 and 65.8–66.9 percent

SiO2; C. Waythomas, unpub. data, 2001). A whole-rock K-Ar age of 342 ka 

was obtained on a scoria bomb (map letter BB). Unit forms spires and 

hoodoos; maximum thickness is about 20 m. Exposed only near the 

confluence of the Chetaslina and East Fork of the Chetaslina Rivers, it is 

interbedded with glaciolacustrine and glacial deposits (unit Qlg) of the 

Copper River Basin. Chemical composition suggests that Mount Drum, 37 

km to north, is a more likely source than Mount Wrangell

BASALTIC ANDESITE–DACITE CENTER

Located between the Dadina and Chichokna Rivers, small eruptive center(s) unconformably 

overlies both, the Jurassic granodiorite of the Chitina batholith (unit Jc) and lava flows possibly 

from the roughly contemporaneous Chetaslina center (unit Qcl). Rocks consist of a series of 

dacite domes, plugs, block and ash deposits, andesite and basaltic andesite flows. Source of the 

flows is unknown, however, whole-rock K-Ar ages suggest that these flows and domes are 

related in time to the Chetaslina lavas, representing pre-modern Wrangell volcanism.

Qah Andesite flows (Pleistocene)—Medium gray, slightly to moderately porphyritic 

andesite flows containing phenocrysts of plagioclase (1–20 percent, as much 

as 3 mm), orthopyroxene (trace–5 percent, as much as 3 mm), hornblende 

(trace–5 percent, as much as 3 mm), and traces of clinopyroxene and olivine 

in a cryptocrystalline to plagioclase (< 0.5 mm) rich groundmass. The 

plagioclase is generally clean and euhedral. Orthopyroxene grows in clots 

with the plagioclase and as single crystals. The hornblende is generally altered 

to black oxide minerals. SiO2 content for two flows (map nos. 51 and 55) 

ranges from 59.2–62.5 percent. Whole-rock K-Ar age is 1,590 ka (map letter 

U). Flows as much as 30 m thick; maximum thickness of unit is probably less 

than 300 m

Qdc Dacite debris apron (Pleistocene)—Blocks and smaller fragments of hornblende 

dacite in crudely layered deposits that dip away from the associated plug spire

Qdi Dacite plugs (Pleistocene)—Light gray, moderately porphyritic hornblende dacite 

plugs containing phenocrysts of plagioclase (5–20 percent; as much as 3 mm), 

hornblende (4–8 percent; as much as 2 mm), and traces of orthopyroxene in a 

cryptocrystalline to microcrystalline groundmass. Plagioclase is generally 

euhedral with inclusion-rich centers and clear rims; hornblende has 

pronounced black oxide rims. The larger of the two plugs forms a prominent 

inaccessible spire near north edge of map area. This plug’s sample was 

obtained from talus (unit Qdc). Both plugs contain 65.1 percent SiO2 (map 

nos. 52, 53); the smaller plug yielded a K-Ar age of 1,640 ka (map letter T)

Qd Dacite flow dome (Pleistocene)—A light gray porphyritic hornblende dacite dome 

containing phenocrysts of plagioclase (10–15 percent, as much as 3 mm) and 

hornblende (3–5 percent, as much as 2 mm) that is locally rimmed with black 
9

oxides, in a cryptocrystalline groundmass. SiO2 content is 64.6 percent (map 

no. 54). The dome, which appears to be one massive flow, is more than 200 m 

thick

Qba Basaltic andesite flows (Pleistocene)—Dark gray, slightly porphyritic basaltic 

andesite flows containing phenocrysts of olivine (3–5 percent, as much as 4 

mm), in clots and as individual rounded crystals, a trace of clinopyroxene in a 

cryptocrystalline groundmass consisting of 70–80 percent plagioclase laths, as 

much as 1 mm long. SiO2 content is 53.7 percent (map no. 56). Unit consists 

of only 2 to 4 thin (5–8 m) flows; maximum thickness is probably less than 30 

m

Qdb Dacite block and ash deposit (Pleistocene)—Contains primarily light gray, 

porphyritic dacite blocks as much as 2 m in diameter in a matrix of light gray 

to very light gray ash. The blocks contain phenocrysts of fresh and euhedral 

plagioclase (15–20 percent, as much as 4 mm), hornblende (1–3 percent, as 

much as 1 mm), orthopyroxene (2–4 percent, as much as 2 mm) and rounded 

clinopyroxene (1–2 percent, as much as 2 mm) in a cryptocrystalline 

groundmass. SiO2 content of dacite block is 65.0 percent (map no. 57)

SHALLOW INTRUSIVE ROCKS

Qod Dacite intrusion (Pleistocene)—Light olive-gray to greenish-gray, porphyritic dacite 

intrusion, containing phenocrysts of plagioclase, hornblende (mostly altered), 

and biotite in a cryptocrystalline groundmass locally flooded by calcite.

Exposed in two small areas along northern margin of quadrangle west of 

Chichokna River. Description from principal exposure to the north in the 

Gulkana A-1 quadrangle where unit intrudes older andesite flows of the 

Chetaslina lavas and where biotite yielded K-Ar age of 1,350 ka (Richter and 

others, 1994)

CHETASLINA LAVAS

Originally named the “Chetaslina vent” lavas by Nye (1983) for a sequence of andesite flows 

that underlie, and are chemically and mineralogically distinct from, the Mount Wrangell shield

lavas. Unit consists primarily of andesite lava flows and breccias, dacite-andesite domes, and 

pyroclastic deposits that locally show the effects of very strong hydrothermal alteration.

However, existence of a major central vent system was not confirmed. Whole-rock K-Ar ages 

indicate that the lavas were erupted between 1,650 and 874 ka.

Qci Andesite dikes (Pleistocene)—Two dikes, of the five observed, were accessible and 

sampled. Both are dark-gray, slightly porphyritic andesite. The freshest 

appearing dike contains phenocrysts of plagioclase, orthopyroxene, and 

clinopyroxene in a microcrystalline groundmass of plagioclase laths. The 

mineralogy and chemistry (61.3 percent SiO2, map no. 59) of this dike and its 

age (545 ka, map letter V) suggests an affinity with Mount Wrangell rather 

than the Chetaslina lavas. The other dike (55.9 percent SiO2, map no. 60) 

contains phenocrysts of plagioclase (5 percent, as much as 3 mm) and 

clinopyroxene (2 percent, as much as 1 mm) in a microcrystalline groundmass 

of plagioclase laths, opaque minerals, and green clay minerals
10

Qcd Andesite-dacite lava domes(?) and breccias (Pleistocene)—Light gray coalescing 

domes(?) ranging from holocrystalline-seriate (crystal mush) andesite to 

porphyritic dacite. The crystal mush (62.0 percent SiO2, map no. 67) contains 

plagioclase (75–90 percent, from <1 mm to as much as 5 mm), orthopyroxene 

(3–8 percent, as much as 2 mm), clinopyroxene (1–2 percent, as much as 2 

mm), and olivine (trace amounts to 1 percent, <1 mm as small rounded 

prisms). The porphyritic dacite (64.8 percent SiO2, map no. 62) contains 

phenocrysts of plagioclase (6–20 percent, as much as 4 mm), clinopyroxene 

(trace amounts to 4 percent, as much as 2 mm), orthopyroxene (1–3 percent, 

as much as 3 mm), and hornblende (trace amounts to 1 percent, as much as 3 

mm) in a cryptocrystalline groundmass. Exposed rocks range from massive, 

dome-like units, as much as 40 m thick, to extremely fragmental units, 

interpreted as carapace breccias, containing blocks as much as a few meters in

diameter. The unit is largely covered by talus. Whole-rock K-Ar age is 874 ka

(map letter W)

Qcl Lava flows, pyroclastic deposits, and breccias, undifferentiated (Pleistocene)—

Primarily a variety of dark brownish-gray andesite lava flows ranging from 

holocrystalline-seriate flows to porphyritic flows, pyroclastic fall deposits, 

and breccias. A holocrystalline-seriate flow (55.7 percent SiO2, map no. 64)

contains plagioclase (70–80 percent, as much as 4 mm), orthopyroxene (1–3

percent, as much as 3 mm) both as single crystals and in clots, olivine (1–3

percent, as much as 3 mm) altered to a brownish clay(?) mineral and minor 

interstitial material. The porphyritic flows (55.3–62.9 percent SiO2, map nos. 

61, 63, 68–70) contain phenocrysts of plagioclase (5–40 percent, as much as 6 

mm), orthopyroxene (3–10 percent, as much as 3 mm), clinopyroxene (1–4

percent, as much as 3 mm), and occasional olivine (0–3 percent) in an altered 

cryptocrystalline groundmass. One highly porphyritic flow (60.8 percent

SiO2, map no. 65) also contains as much as 1 percent fresh biotite in clusters 

as much as 2 mm in diameter and 1 percent black oxide ghosts of hornblende 

crystals. Weakly indurated, light green, mauve, and cream colored pyroclastic 

fall(?) deposits locally form a landscape of spires and hoodoos that easily 

break down into a mud-rich slurry. A few laharic(?) breccias were noted 

during aerial observation of the more rugged area of the Chetaslina terrain. 

One possible vent breccia (64.3 percent SiO2, map no. 66) contains abundant 

clasts of plagioclase porphyry and small (<5 mm) clasts of fine-grained 

siltstone or chert in a matrix of broken plagioclase crystals, altered hornblende 

laths, clinopyroxene, and altered cryptocrystalline material. Nye (1983) 

reported whole-rock K-Ar ages of 1,580 ka and 980 ka for andesitic lava 

flows in this unit (map letters X and Y); two additional whole-rock K-Ar ages 

of 1,650 ka (map letter Z) and 867 ka (map letter AA) were obtained during 

this study

SEDIMENTARY ROCKS 

Qcg Conglomerate (Pleistocene)—Slightly indurated pebble to boulder fluvial 

conglomerate with interbedded lenses of sandstone. Appears to fill a paleovalley on Chetaslina lavas (unit Qcl). This conglomerate is a continuation of a 
11

more extensive sedimentary rock unit mapped in the contiguous Gulkana A-1 

quadrangle (Richter and others, 1994)

MESOZOIC AND PALEOZOIC ROCKS

The distribution of these basement rocks, as shown on the geologic map, is taken with minor 

modification from Winkler and others (1981, 1995); the descriptions, with minor additions, are 

taken from Winkler and others (1995).

Ks Marine sedimentary rocks (Early Cretaceous)—Consists of the Berg Creek 

Formation and unnamed marine sedimentary rocks. Primarily glauconitic and 

fossiliferous siltstone, sandstone, and conglomerate

Jc Chitina Valley batholith (Late Jurassic)—Weakly to strongly foliated quartz 

monzodiorite, quartz diorite, tonalite, and granodiorite

Jc Marine clastic and carbonate rocks, undivided (Late or Middle Jurassic to Late 

Triassic)—Consists of the Kotsina Conglomerate (Late or Middle Jurassic), 

the lower member of the McCarthy Formation (Late Triassic), and the 

Chitistone and Nizina Limestones (Late Triassic). The Kotsina Conglomerate 

is a thick-bedded cobble to pebble conglomerate containing lenses of 

sandstone, siltstone, and carbonaceous shale. The lower member of the 

McCarthy Formation consists of impure limestone, shale, and chert that 

gradationally overlies thin- and thick-bedded limestones of the Chitistone and 

Nizina Limestones

Jm Haley Creek metamorphic assemblage (Late Jurassic and Pennsylvanian or 

older?)—Consists of the Uranatina River metaplutonic unit (Jurassic and 

Pennsylvanian) and the Strelna Metamorphics of Plafker and others (1989)

(Early Pennsylvanian and older?). Low- to medium-grade (greenschist to 

amphibolite facies) metamorphic rocks tentatively considered to represent 

roots of Skolai magmatic arc

n Nikolai Greenstone (Late and (or) Middle Triassic)—Chiefly subaerial tholeiitic 

flood basalts 

Ps Skolai Group (Early Permian and Pennsylvanian)—Volcanic, volcaniclastic, and 

sedimentary rocks of a late Paleozoic magmatic arc
12

References Cited

Benson, C.S., and Follett, A.B., 1986, Application of photogrammetry to the study of volcano-glacier 

interactions on Mount Wrangell, Alaska: Photogrammetric Engineering and Remote Sensing, v. 52, 

no. 6, p. 813–827.

Benson, C.S., and Motyka, R.J., 1979, Glacier-volcano interactions on Mt. Wrangell, Alaska: Fairbanks, 

University of Alaska, Annual Report, Geophysical Institute p. 1–25.

Clarke, G.K.C., Cross, G.M., and Benson, C.S., 1989, Radar imaging of glaciovolcanic stratigraphy, 

Mount Wrangell caldera, Alaska—Interpretation model and results: Journal of Geophysical Research, 

v. 94, p. 7,237–7,249.

Ferrians, O.J., Jr., 1989, Glacial Lake Atna, Copper River Basin, Alaska, in Carter, L.D., Hamilton, 

T.D., and Galloway, J.P., eds., Late Cenozoic history of the interior basins of Alaska and the Yukon:

U.S. Geological Survey Circular 1026, p. 85–88.

Furst, M.J., 1968, The reconnaissance petrology of andesites from the Mt. Wrangell caldera, Alaska: 

Fairbanks, University of Alaska, M.S. thesis, 83 p.

MacKevett, E.M., Jr., 1978, Geologic map of the McCarthy quadrangle, Alaska: U.S. Geological 

Survey Miscellaneous Investigations Series Map I–1032, scale 1:250,000.

Mendenhall, W.C., and Schrader, F.C., 1903, The mineral resources of the Mount Wrangell district, 

Alaska: U.S. Geological Survey Professional Paper 15, 71 p.

Neal, C.A., Herrick, J., Girina, O.A., Chibisova, M., Rybin, A., McGimsey, R.G., and Dixon, J., 2014, 

2010 volcanic activity in Alaska and Kamchatka—Summary of events and response of the Alaska 

Volcano Observatory: U.S. Geological Scientific Investigations Report 2014–5034, 76 p.

Nye, C.J., 1983, Petrology and geochemistry of Okmok and Wrangell volcanoes, Alaska: Santa Cruz, 

University of California, Ph.D. dissertation, 208 p.

Plafker, G., Nokleberg, W.J., and Lull, J.S., 1989, Bedrock geology and tectonic evolution of the 

Wrangellia, Peninsular, and Chugach terranes along the Trans-Alaska Crustal Transect in the 

Chugach Mountains and southern Copper River basin, Alaska: Journal of Geophysical Research, v. 94 

p. 4,255–4,295.

Powell, A.M., 1900, The Gakona and Chistochina Rivers, in United States Congress, Senate Committee 

on Military Affairs, Compilation of narratives of explorations in Alaska: Washington, D.C.,

Government Printing Office, p. 783.

Rice, J.F., 1900, From Valdez to Eagle City, in United States Congress, Senate Committee on Military 

Affairs, Compilation of narratives of explorations in Alaska: Washington, D.C., Government Printing 

Office, p. 788.

Richter, D.H., Duffield, W.A., Sawyer, D.A., Ratté, J.C., and Schmoll, H.R., 1994, Geologic map of the 

Gulkana A-1 quadrangle, south-central Alaska: U.S. Geological Survey Geologic Quadrangle Map 

GQ–1728, scale 1:63,360.

Richter, D.H., Moll-Stalcup, E., Duffield, W.A., and Shew, Nora, 1997, Geologic map of the Nabesna 

A–6 quadrangle, Alaska: U.S. Geological Survey Open File Report 97–475, scale 1:63,360.

Richter, D.H., Preller, C.C., Labay, K.A., and Shew, N.B., compilers, 2006, Geologic map of the 

Wrangell-Saint Elias National Park and Preserve, Alaska: U.S. Geological Survey Scientific 

Investigations Map 2877, scale 1:350,000.

Richter, D.H., Rosenkrans, D.S., and Steigerwald, M.J., 1995, Guide to the volcanoes of the western 

Wrangell Mountains, Alaska—Wrangell-St. Elias National Park and Preserve: U.S. Geological 

Survey Bulletin 2072, 31 p.
13

Richter, D.H., Smith, R.L., Yehle, L.A., and Miller, T.P., 1979, Geologic map of the Gulkana A-2 

quadrangle, Alaska: U.S. Geological Survey Geologic Quadrangle Map GQ–1520, scale 1:63,360.

Tarr, R.S., and Martin, Lawrence, 1912, The earthquakes at Yakutat Bay, Alaska in September, 1899: 

U.S. Geological Survey Professional Paper 69, 135 p.

Waythomas, C.F., and Wallace, K.L., 2002, Flank collapse at Mount Wrangell, Alaska, recorded by 

volcanic mass-flow deposits in the Copper River lowland: Canadian Journal of Earth Sciences, v. 39, 

p. 1257–1279.

Winkler, G.R., Goldfarb, R.J., and Borden, J.C., 1995, Map showing geology and geochemically 

anomalous areas, Valdez 1°×3° quadrangle, south-central Alaska, in Goldfarb, R.J., Borden, J.C., and 

Winkler, G.R., Geochemical survey of the Valdez 1°

×3° quadrangle, south-central Alaska: U.S. 

Geological Survey Bulletin 2084, scale 1:250,000.

Winkler, G.R., Silberman, M.L., Grantz, Arthur, Miller, R.J., and MacKevett, E.M., Jr., 1981, Geologic 

map and summary geochronology of the Valdez quadrangle, southern Alaska: U.S. Geological Survey 

Open-File Report 80–892–A, 2 sheets, scale 1:250,000.

Yehle, L.A., and Nichols, D.R., 1980, Reconnaissance map and distribution of the Chetaslina volcanic 

debris flow (new name), southeastern Copper River Basin and adjacent areas, south-central Alaska: 

U.S. Geological Survey Miscellaneous Field Studies Map MF–1209, scale 1:250,000.
14

Figure 1. Generalized map showing present extent of Mount Wrangell lavas (red), Valdez D-1 and D-2 

quadrangles, and sample locations (dots) outside Valdez D-1 and D-2 map area. All other rocks are tan, surficial 

deposits are yellow, ice is white, and rivers are blue.
15

Figure 2. Total alkalis (Na2O+K2O) versus silica content for volcanic rocks from the Valdez D-1 and D-2 

quadrangles, Alaska.
16

Table 1. Chemical analyses of volcanic rocks from the Valdez D-1 and D-2 quadrangles, Alaska.

[Analyses by U.S. Geological Survey x-ray fluorescence methods, D. Siems, analyst. Data are normalized volatile-free; %, percent, LOI, lost on ignition. Samples of map numbers 

31 and 32 are from the contiguous Valdez C-1 quadrangle; see fig. 1]

Map no. Field no. %SiO2 %Al2O3 %FeTO3 %MgO %CaO %Na2O %K2O %TiO2 %P2O5 %MnO LOI Original

total Latitude_NAD27 Longitude_NAD27

Lava flows of the Mount Wrangell shield (unit Qw)

1 99ARh-1 62.2 16.3 5.59 3.24 5.38 3.76 2.34 0.88 0.24 0.09 0.85 99.65 61.836775 -144.430902

2 99ARh-3 62.0 16.2 5.70 3.37 5.41 3.77 2.31 0.89 0.25 0.09 0.88 99.34 61.849147 -144.346688

3 99ARh-4 61.9 16.7 5.61 3.03 5.54 3.95 2.05 0.89 0.26 0.09 0.03 100.02 61.858423 -144.249289

4 99ARh-21 62.2 15.9 5.77 3.42 5.35 3.72 2.35 0.90 0.24 0.09 0.85 99.28 61.814307 -144.362716

5 99ARh-34 61.6 16.7 5.76 3.16 5.67 3.99 1.97 0.90 0.26 0.09 0.12 100.24 61.846570 -144.130270

6 99ARh-35 62.0 16.8 5.84 2.19 5.37 4.27 2.11 1.02 0.28 0.08 <0.01 100.45 61.851872 -144.100505

7 99ARh-36A 60.0 16.3 6.37 4.24 6.01 3.72 1.95 0.98 0.27 0.10 <0.01 100.59 61.885998 -144.058912

8 99ARh-36B 60.5 16.4 5.77 4.35 6.10 3.75 1.92 0.82 0.27 0.09 0.45 99.97 61.888485 -144.055729

9 99ARh-38 61.7 16.3 5.84 3.50 5.59 3.77 2.06 0.88 0.25 0.10 <0.01 100.62 61.859030 -144.015503

10 99ARh-39 62.4 16.6 5.80 2.15 5.10 4.35 2.17 1.04 0.30 0.08 0.26 100.12 61.868942 -144.089600

11 99ARh-50 60.6 17.1 5.93 3.59 6.11 3.74 1.76 0.80 0.23 0.09 0.20 99.95 61.908267 -144.188244

12 99ARh-51 61.5 16.3 5.99 3.37 5.64 3.93 1.97 0.89 0.26 0.10 <0.01 100.46 61.880195 -144.162325

13 00ARh-1 62.2 16.5 5.65 3.13 5.49 3.64 2.10 0.87 0.27 0.09 0.83 98.66 61.974834 -144.347116

14 00ARh-3 62.3 16.2 5.69 3.38 5.34 3.50 2.36 0.88 0.25 0.09 0.79 98.84 61.799234 -144.416363

15 00ARh-6B 62.2 17.1 5.73 2.26 5.40 3.94 2.06 1.00 0.29 0.08 0.16 100.19 61.843060 -144.102813

16 00ARh-9 60.9 17.4 5.79 3.55 6.28 3.59 1.42 0.72 0.27 0.10 0.03 100.53 61.829225 -144.117022

17 00ARh-10 61.7 16.9 5.60 3.04 5.69 3.78 2.00 0.90 0.29 0.09 0.12 99.48 61.817767 -144.164045

18 00ARh-13 61.8 17.1 5.37 3.18 5.85 3.67 1.96 0.81 0.25 0.08 0.39 99.08 61.793159 -144.113714

19 00ARh-14 62.3 16.9 5.23 2.95 5.64 3.66 2.10 0.83 0.27 0.08 0.30 99.32 61.783035 -144.155463

20 00ARh-15D 61.0 17.0 5.88 3.61 6.05 3.51 1.78 0.81 0.25 0.09 0.12 99.72 61.928401 -144.169873

21 00ARh-21 62.5 16.7 5.42 3.15 5.60 3.67 1.88 0.73 0.27 0.09 -0.04 100.25 61.979877 -144.234252

22 00ARh-36 62.1 16.6 5.59 3.32 5.45 3.53 2.21 0.87 0.26 0.09 0.02 100.29 61.812396 -144.410406

23 00ARh-37 61.9 16.9 5.43 3.21 5.77 3.64 2.00 0.83 0.26 0.09 0.73 99.52 61.798683 -144.236696

24 99ARh-46 63.3 17.2 4.79 2.47 5.24 3.95 2.19 0.62 0.19 0.08 0.84 99.55 61.918012 -144.290253

25 99ARh-46A 62.9 16.6 5.23 2.78 5.30 4.02 2.03 0.80 0.24 0.08 0.06 99.98 61.921715 -144.290973

26 00ARh-17 62.3 16.9 5.11 3.65 5.75 3.81 1.62 0.61 0.21 0.08 0.49 99.43 61.933666 -144.263651

27 00ARh-17A 62.2 16.4 5.78 3.09 5.45 3.77 2.03 0.92 0.28 0.09 0.62 99.38 61.932315 -144.254155

28 00ARh-29 62.5 16.6 5.47 2.96 5.48 3.71 2.06 0.85 0.26 0.09 0.89 98.59 61.932315 -144.254155
17

Map no. Field no. %SiO2 %Al2O3 %FeTO3 %MgO %CaO %Na2O %K2O %TiO2 %P2O5 %MnO LOI Original

total Latitude_NAD27 Longitude_NAD27

45 00ARh-32 62.0 16.4 5.79 3.46 5.56 3.55 2.05 0.84 0.27 0.09 1.20 98.98 61.867509 -144.307267

Mount Wrangell valley-fill and basin lava (unit Qwv)

29 99ARh-5 60.9 17.0 5.89 3.54 6.01 3.80 1.82 0.82 0.23 0.09 0.06 100.24 61.871938 -144.239077

30 99ARh-22 61.4 17.1 5.82 2.34 5.72 4.18 2.07 1.01 0.28 0.08 0.62 99.74 61.764326 -144.678139

31 99ARh-24 61.6 16.5 5.68 3.42 5.74 3.87 1.97 0.84 0.23 0.09 0.01 100.44 61.572031 -144.344307

32 99ARh-25 61.7 16.7 5.61 3.35 5.72 3.82 1.97 0.83 0.24 0.09 0.11 100.30 61.724658 -144.312002

33 99ARh-29 61.4 17.0 5.96 2.28 5.70 4.23 2.03 1.04 0.29 0.09 <0.01 100.02 61.853464 -144.409143

34 99ARh-49 63.6 16.0 5.78 1.78 4.43 4.41 2.50 1.12 0.34 0.08 0.13 100.04 61.893844 -144.276322

35 99ARh-49B 62.4 16.6 5.63 2.32 5.30 4.13 2.30 1.02 0.29 0.08 <0.01 100.22 61.892714 -144.275007

36 99CW-16-1 61.6 16.9 5.93 2.24 5.55 4.24 2.09 1.05 0.30 0.08 0.09 100.35 61.847668 -144.616789

37 00ARh-7 61.6 16.6 5.74 3.56 5.78 3.58 1.93 0.82 0.25 0.09 -0.01 99.95 61.854315 -144.115832

38 00ARh-11 62.4 16.8 5.78 2.21 5.24 4.02 2.14 1.02 0.31 0.08 -0.06 99.63 61.811127 -144.199913

39 00ARh-12 61.6 16.7 5.79 3.55 5.78 3.57 1.93 0.83 0.25 0.09 0.18 100.23 61.789347 -144.341701

40 00ARh-15 61.0 17.0 5.88 3.56 6.05 3.55 1.80 0.80 0.24 0.09 -0.15 99.46 61.909922 -144.173307

41 00ARh-16 60.7 17.1 5.92 3.67 6.18 3.52 1.71 0.80 0.24 0.09 -0.19 99.79 61.940724 -144.188589

42 00ARh-19A 60.9 16.7 5.66 4.15 6.24 3.40 1.87 0.73 0.26 0.09 0.94 99.36 61.899632 -144.278147

43 00ARh-26 60.5 18.0 5.54 2.76 6.42 3.78 1.78 0.89 0.28 0.08 -0.06 100.79 61.864780 -144.344218

44 00ARh-27 61.0 17.1 5.82 3.51 6.06 3.55 1.81 0.81 0.25 0.09 0.89 98.73 61.861634 -144.329258

46 00Mc-1 61.1 16.4 6.14 3.80 5.75 3.46 2.13 0.90 0.26 0.10 0.84 98.90 61.787685 -144.687394

47 00Mc-2 61.1 17.5 5.72 2.60 6.06 3.83 1.94 0.96 0.29 0.09 0.49 100.23 61.845670 -144.575096

48 00Mc-6 61.7 17.0 5.91 2.34 5.64 3.96 2.05 1.03 0.31 0.09 -0.12 100.16 61.857053 -144.476964

49 00Mc-8 61.8 16.4 5.77 3.37 5.55 3.57 2.26 0.91 0.25 0.09 1.03 98.69 61.790347 -144.388087

Early Wrangell lava (unit Qwe)

50 99ARh-30 57.4 16.3 6.93 5.58 6.93 3.33 2.08 0.99 0.33 0.11 0.04 99.98 61.894815 -144.455661

Basaltic andesite–dacite center (units Qdi, Qd, Qah, Qba, Qdb, Qdc)

51 00ARh-35 59.2 17.7 6.54 3.90 6.60 3.75 1.07 0.80 0.32 0.11 0.95 99.34 61.993355 -144.469528

52 00ARh-5 65.1 17.2 4.12 2.21 5.02 3.91 1.61 0.50 0.21 0.07 1.74 98.24 61.985265 -144.420422

53 00ARh-38 65.1 17.0 4.13 2.56 5.09 4.10 1.30 0.45 0.21 0.07 0.51 99.05 61.997437 -144.469470

54 99ARh-16 64.6 17.2 4.26 2.32 5.00 4.15 1.74 0.50 0.19 0.08 0.21 100.17 61.957773 -144.478846

55 00ARh-4A 62.5 17.0 5.42 2.95 5.49 3.84 1.64 0.78 0.29 0.09 -0.08 100.37 61.972338 -144.489955

56 99ARh-17A 53.7 16.1 8.39 6.79 8.31 3.35 1.50 1.32 0.40 0.13 0.23 99.99 61.989096 -144.486966

57 99ARh-17 65.0 17.2 4.15 1.90 4.85 4.37 1.77 0.50 0.20 0.07 1.41 98.68 61.991325 -144.477399

Chetaslina lava (units Qci, Qcd, Qcl)

58 00ARh-39 57.7 17.7 6.68 4.66 7.07 3.49 1.50 0.78 0.26 0.11 0.51 99.81 61.942863 -144.310637
18

Map no. Field no. %SiO2 %Al2O3 %FeTO3 %MgO %CaO %Na2O %K2O %TiO2 %P2O5 %MnO LOI Original

total Latitude_NAD27 Longitude_NAD27

59 00ARh-33A 61.3 16.8 5.64 3.91 6.12 3.42 1.76 0.75 0.25 0.09 1.17 98.77 61.937059 -144.229123

60 00ARh-23A 55.9 18.7 8.14 3.80 7.33 3.83 0.43 1.39 0.38 0.07 4.05 95.54 61.997131 -144.420959

61 99ARh-48B 62.9 17.3 4.95 2.70 5.53 4.17 1.54 0.65 0.20 0.08 0.15 99.92 61.910364 -144.326228

62 99ARh-8 64.8 16.0 5.16 1.64 4.12 4.48 2.38 0.90 0.35 0.09 0.34 99.78 61.895112 -144.364564

63 99ARh-10 55.3 18.2 7.64 4.93 7.80 3.78 0.95 1.00 0.27 0.12 <0.01 100.66 61.890393 -144.379562

64 99ARh-15 55.7 18.1 7.48 4.80 7.87 3.68 0.94 1.00 0.29 0.12 0.94 99.43 61.914477 -144.356427

65 00ARh-18A 60.8 15.8 5.36 4.05 5.72 3.94 2.93 0.89 0.37 0.08 1.95 98.49 61.911093 -144.277549

66 00ARh-23B 64.3 16.8 4.77 2.52 5.51 3.41 1.69 0.66 0.24 0.06 2.46 96.99 61.996851 -144.425325

67 99ARh-9 62.0 17.2 5.52 2.98 5.52 4.03 1.69 0.76 0.24 0.09 0.06 100.17 61.892638 -144.373396

68 00ARh-23D 57.8 16.6 6.53 5.46 7.14 3.37 1.55 1.03 0.39 0.11 1.19 98.21 61.993140 -144.434742

69 00ARh-31 61.7 16.8 5.79 3.07 5.61 3.73 1.95 0.97 0.33 0.08 1.45 98.11 61.953372 -144.206241

70 00ARh-33 62.4 16.7 5.47 3.15 5.44 3.66 2.06 0.87 0.27 0.07 1.38 97.83 61.939285 -144.232037

Andesite plug of Mount Wrangell (unit Qwp)

71 99ARh-44 62.4 16.7 5.36 2.89 5.42 3.99 2.04 0.85 0.25 0.09 0.16 99.99 61.939110 -144.315647

Andesite lava flows of Mount Drum (unit Qdl)

72 99ARh-19 60.8 17.0 5.49 4.58 5.97 3.68 1.58 0.55 0.19 0.09 1.00 99.28 61.979812 -144.671920

Young Wrangell pumice

73 00ARh-40 60.6 17.1 5.90 3.80 6.23 3.62 1.61 0.79 0.25 0.09 -0.06 99.99 61.981695 -144.242873
19

Table 2. Radiometric ages from map units in the Valdez D-I and D-2 quadrangles, Alaska.

[Ages listed for map letters A, G, H, I, R, X, and Y have been reported previously (Nye, 1983). All other ages are new. Sample at map letter N is from the Long Valley flow in the 

contiguous Valdez C-1 quadrangle; see fig. 1]

Map letter Sample no. K2O% 40Arrad/gm 40Arrad% Calc. age (ka) Analyst Latitude_NAD27 Longitude_NAD27

Lava flows of the Mount Wrangell shield (unit Qw)

A 79cne-29 2.158+0.005 13.00 x 10-13 5.40 420+30 D.L. Turner 61.979949 -144.301892

B 80cnh-16 2.115+0.010 8.45 x 10-13 10.15 280+13 D.L. Turner 61.927152 -144.172793

8.58 x 10-13 10.27

C 99ARh-43 0.890+0.006 8.475 x 10-13 5.70 662+45 M.A. Lanphere 61.933666 -144.263651

D 99ARh-51 2.164+0.011 16.08 x 10-13 42.10 516+8 M.A. Lanphere 61.880195 -144.162325

E 00ARh-8 2.422+0.250 3.153 x 10-13 3.50 90+15 M.A. Lanphere 61.832683 -144.110183

F 00ARh-14 2.188+0.013 4.449 x 10-13 1.00 141+59 M.A. Lanphere 61.783035 -144.155463

O 99ARh-36B 2.088+0.004 1.506 x 10-13 1.60 50+13 M.A. Lanphere 61.888485 -144.055729

CC 99ARh-41 2.2975+0.005 4.05 x 10-13 10.92 124.8+5.2 A.T. Calvert 61.860979 -144.092201

4.19 x 10-13 11.91

Mount Wrangell valley-fill and basin lavas (unit Qwv)

G 79cnc-1 2.043+0.015 7.900 x 10-13 1.80 270+40 D.L. Turner 61.847668 -144.616789

H 79cnd-2 2.014+0.012 12.50 x 10-13 1.80 430+80 D.L. Turner 61.787685 -144.687394

I 79cnf-1 1.943+0.022 2.100 x 10-13 1.30 80+20 D.L. Turner 61.974947 -144.209392

J 80cnh-18 1.820+0.000 0.680 x 10-13 2.98 25+8 D.L. Turner 61.857053 -144.476964

0.610 x 10-13 2.66

K 80cnh-19 1.792+0.002 2.790 x 10-13 4.93 105+10 D.L. Turner 61.866162 -144.403092

2.650 x 10-13 4.68

L 90ARh-7 1.656+0.005 1.635 x 10-13 2.20 76+15 Nora Shew 61.758436 -144.654839

2.020 x 10-13 2.30

M 99ARh-5 1.970+0.003 2.298 x 10-13 4.80 81+9 M.A. Lanphere 61.871938 -144.239077

N 99ARh-23 2.158+0.004 3.600 x 10-13 6.60 116+9 M.A. Lanphere 61.570117 -144.315607

P 00ARh-26 1.891+0.007 3.320 x 10-13 7.30 122+9 M.A. Lanphere 61.864780 -144.344218

Q 00Mc-2 2.014+0.001 11.00 x 10-13 3.80 378+39 M.A. Lanphere 61.845670 -144.575096

Early lava flows of Mount Wrangell (unit Qwe)

R 79cne-3 2.233+0.013 22.10 x 10-13 9.60 690+30 D.L. Turner 61.967410 -144.295892

Andesite plug of Mount Wrangell (unit Qwp)

S 99ARh-44 2.088+0.007 15.91 x 10-13 57.70 529+7 M.A. Lanphere 61.939110 -144.315647

Basaltic andesite-dacite center, dacite plugs (unit Qdi)

T 00ARh-38 1.359+0.004 32.07 x 10-13 48.40 1,640+20 M.A. Lanphere 61.997437 -144.469470
20

Map letter Sample no. K2O% 40Arrad/gm 40Arrad% Calc. age (ka) Analyst Latitude_NAD27 Longitude_NAD27

Basaltic andesite-dacite center, andesite flow (unit Qah)

U 00ARh-4A 1.742+0.008 40.00 x 10-13 53.20 1,590+16 M.A. Lanphere 61.972338 -144.489955

Andesite dikes (Chetaslina or Mount Wrangell, unit Qci)

V 00ARh-33 2.181+0.002 17.10 x 10-13 43.60 545+8 M.A. Lanphere 61.939285 -144.232037

Dacite dome (Chetaslina lavas, unit Qcd)

W 99ARh-9 1.726+0.003 21.72 x 10-13 66.20 874+10 M.A. Lanphere 61.892638 -144.373396

Lava flows (Chetaslina lavas, unit Qcl)

X 79cne-1 0.962+0.006 21.80 x 10-13 6.70 1,580+30 D.L. Turner 61.964350 -144.300292

Y 79cnf-2 2.125+0.017 30.10 x 10-13 10.10 980+30 D.L. Turner 61.957716 -144.198970

Z 00ARh-23D 1.514+0.014 37.40 x 10-13 55.00 1,650+17 M.A. Lanphere 61.993140 -144.434742

AA 00ARh-39 1.511+0.010 18.90 x 10-13 8.90 867+38 M.A. Lanphere 61.942863 -144.310637

Pyroclastic flow (unit Qpf)

BB 90ARh-7A 0.393+0.003 1.885 x 10-13 2.80 342+16 Nora Shew 61.757048 -144.655190

1.981 x 10-13 3.40