Geolc>gy of the Mount 

Katmai Area 

Alaska 

!1y A. SAMUEL KELLER and HILLARD N. REISER 

VIINERAL RESOURCES OF ALASKA 

3EOLOGICAL SURVEY BULLETIN 1058-G 

NITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959 
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

For sale by the Superintendent of Documents, U.S. Government Printin~ Office 

Washington 25, D.C. 
CONTENTS 

Page 

Abstract ____ ~---------------------------------------------------- 261 

Introduction------------------------------------------------------ 262 Geologic methods_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 263 

Previouswork________________________________________________ 263 

Acknowledgments_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 264 

Geomorphology_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 264 

TopographY-------------------------------------------------- 264 Drainage _________________ -,-__________________________________ 265 

Ftivers___________________________________________________ 265 

Lakes____________________________________________________ 266 

Glaciation____________________________________________________ 266 

Coastlines____________________________________________________ 267 

Recent volcanism_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 268 

StratigraphY------------------------------------------------------ 268 

Undifferentiated rocks older than Middle Jurassic._________________ 268 

Bedded rocks of Mesozoic age__________________________________ 269 

Naknek formation_________________________________________ 269 

Kaguyak formation________________________________________ 273 

Bedded rocks of Cenozoic age:-- ___ --------______________________ 278 

Coal-bearing rocks ___________________________________ -----_ 278 

Volcanic flows and associated rocks ____________________ ----__ 282 

Tuff_____________________________________________________ 286 

Surficial deposits_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 286 

Intrusiverocks _________________ ~---------------------------------- 287 

Jurassic age _____________ ---~__________________________________ 287 

Tertiary age-------------------------------------------------- 287 

Structure--------------------------------------------------------- 288 Structuralfeatures_____________________________________________ 288 

Age of the folding and faulting ________________ .., ·- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 290 

Historical geology ______________ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 290 

Petroleum possibilities __________ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 291 

Stratigraphic relations _______ :-__________________________________ 292' 

Structural relations ___________________________ ·-________________ 293: 

Selected references_________________________________________________ 295. 

Index------------------------------------------------------------ 297· 

Ill 
IV CONTENTS 

ILLUSTRATIONS 

Page 

PLATE 29. Geologic map and structure sections, Mount Katmai area __ In pocket 30. Hallo Bay glacier __________________________________ Facing 264 

31. Fiordlike bays of Shelikof Strait---------------------- Facing 265 

32. Graphic stratigraphic sections _________________________ In pocket 

FIGURE 44. Index map of Alaska, showing location of Mount Katmai area_ 262 

45. Correlation chart of formations in the Mount Katmai area___ Z'/4 

46. Comparison of Naknek and older formations_ _ _ _ _ _ _ _ _ _ _ _ _ _ 294 
MINERAL RESOURCES OF ALASKA 

GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 

By A. SAMUEL KELLER and HILLARD N. REISER 

ABSTRACT 

The Mount Katmai area is on the Alaska Peninsula and comprises the Mount 

Katmai quadrangle, the Cape Douglas area of the adjoining Afognak quadrangle, 

and parts of the Karluk and Naknek quadrangles. The area, which includes 

nearly all the Katmai National Monument, is one of high relief and is drained 

by streams of preglacial origin. At least two ice advances are indicated by 

the moraine configuration. Present-day glaciation is restricted to numerous 

alpine glaciers in the mountain areas. Fifteen recently active volcanoes roughly 

form a line from Mount Douglaa to Martin Mountain. 

Sedimentary rocks older than Middle Jurassic age, and of Late Jurassic, 

Late Cretaceous, and Eocene age are represented. Silicic and mafic igneous 

rocks of Early and (or) Middle Jurassic and Tertiary age locally intrude the 

sedimentary rocks. Volcanic rocks, chiefly andesite and basalt of Tertiary and 

Quaternary age, locally overlie the formations of Late Jurassic and Late Cretaceous age. The Naknek formation of Late Jurassic age comprises a conglomerate unit overlain by 6,000 to H,OOO feet of fossiliferous sandstone, siltstone, conglomerate, and shale. A new formation, the Kaguyak formation, of 

Late Cretaceous (Campanian-Maestrichtian) age is proposed. The formation 

has been divided into three informal members : a lower ± 2,0QO-foot fossiliferous 

siltstone :member, a middle 1,090-foot sandstone, siltstone, and shale member, 

and an upper +1,460-foot littoral sandstone and siltstone member. A largely 

nonmarine coal-bearing formation at least 830 feet thick consists of conglomerate, sandstone, siltstone, shale, and coal, and interfingers with layered 

volcanic rocks of Eocene age. 

Seven northeastward-trending .anticlines locally interrupt the regional southeasterly dip of the sedimentary rocks. The largest is the Kamishak anticline, 

whose crest is intruded by a q"Qartz diorite stock. A reverse fault transects 

the mapped area from the Little Kamishak River to Contact Creek. 

The roeks of the Naknek formation were derived in part from Lower and 

(or) Middle Jurassie intrusive rocks and were laid down as shelf deposits during a transgression of seas dulling Late Jurassic time. The area was at a 

state of base level during most o~ Cretaceous time. The seas transgressed during Late Cretaceous time, and tbis was followed by a major regression of the 

seas permitting the area to emerge completely during Eocene time. No major 

deformation occurred during Jurassic and Cretaceous time and since then there 

has been only one major period of folding and faulting, probably after Eocene 

and before Quaternary time. 

261 
262 M~ERAL RESOURCES OF ALASKA 

Sedimentary rocks of the Naknek and Kaguyak formations may serve as 

both a source and a reservoir for petroleum. Locally, structural and stratigraphic traps may also be present. Any exploitation of the area for petroleum 

seems remote, however, and probably should not be attempted until such time 

as drilling in more favorable localities north and south of the Mount Katmai 

area delimits the petroleum possibilities of the sedimentary rocks. 

INTRODUCTION 

During the 1954 field season the authors made reconnaissance 

studies in the Mount Katmai quadrangle and adjacent areas. The 

map area (fig. 44), which includes nearly all the Katmai National 

Monument, is on the Alaska Peninsula approximately between lat 

58°00' N. and 59°00' N. It is bounded on the west approximately 

FIGURE 44.-Index map of Alaska, showing location of Mount Katmai area (shaded). 

by long 156°00' W. and on the east by Shelikof Strait, and covers 

about 5,000 square miles. The field season began July 1, 1954, and 

ended on September 2, 1954. These geologic investigations were made 

in collaboration with the U.S. National Park Service as part of a 

scientific program designed to evaluate the various geological, biological, botanical, and archeological features of Katmai N a tiona) 

Monument. 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 263 

GEOLOGIC METHODS 

The area was mapped on vertical aerial photographs at a scale of 

1 : 40,000. These geologic data were later transferred to a base map 

of 1 : 250,000 scale. The use of aerial photographs facilitated mapping and allowed the geologists to cover a considerably greater area 

than would otherwise be possible in a short field season. During 

the course of the work eight field camps were established. These 

camps were reached by float plane supplied by the U.S. Air Force. 

From these base ca.mps, geologic investigations were made by foot 

traverse as far as practical. In addition to the time that was spent 

on the ground, a part of the season was devoted to an aerial reconnaissance of the area. 

PREVIOUS WORK 

Since 1898 many scientists have contributed to the knowledge of 

the area mapped. In that year, J. E. Spurr crossed the Alaska 

Peninsula from Naknek on the west coast to Katmai Bay on the east, 

and his studies of the geology in the vicinity of Mount Katmai and 

elsewhere were published in 1900. B. K. Emerson and Charles 

Palache, members of the Harriman Alaska Expedition of 1899, 

landed at several points along Shelikof Strait and made collections 

of plant fossils from the rocks of Eocene age at Cape N ukshak. 

Their findings were published in 1904. W. ·V\r. Atwood in 1911 published the results of reconnaissance work in 1.908 along parts of the 

coastline of the area mapped by the authors. In 1923, K. F. Mather 

made a reconnaissance study of the rocks from Iliamna Bay to the 

Savonoski River, and during the same year W. R. Smith joined 

Mather's party at the Savonoski River after making a geologic study 

of the area from Cold Bay (now Puale Bay) to Mount Katmai. 

The studies of both Mather and Smith were published in 1925. The 

eruption of Mount Katmai in 1912 and the ernplacement of the tuff 

in the Valley of Ten Thousand Smokes are treated in publications 

by R. F. Griggs (1922} and C. N. Fenner (1920, 1922, 1923, 1925). 

In more recent years, J. C. Hazzard and others (1950} of the 

Union Oil Company of California and the Ohio Oil Company published the results of their findings near Kamishak Bay and Cape 

Kaguyak. The glacial geology of parts of the area are included in 

publications by E. H. Muller (1952, 1953, 1954}. Also, within the 

past 5 years, studies of volcanology and geomorphology have been 

made by Garniss Curtis, and to a lesser extent by Rowel Williams, 

J. B. Lucke, H. W. Coulter, and G. L. Snyder. Summary statements by these men are available in a report by the National Park 

Service (Luntey and others, 1954). 
264 MINERAL RESOURCES OF ALASKA 

In 1953, R. Werner J uhle, a geologist of the U.S. Geological Survey, 

lost his life while engaged in scientific investigations in Katmai 

National Monument. J uhle's field notes and those of his assistant, 

Ronald W. Kistler, have been used in the preparation of this report, 

and their mapping in the vicinity of Mount Katmai has been 

included on plate 29. 

ACKNOWLEDGMENTS 

The authors wish to acknowledge the aid of Robert S. Luntey of 

the National Park Service, who acted as an agent for liaison between 

the Geological Survey and the U.S. Air Force, and provided the 

logistic support necessary for the completion of the geologic studies. 

The authors wish also to thank the pilots of the U.S. Air Force at 

King Salmon, Alaska, who often flew under trying conditions in 

order to supply the needs of the geologists. They are indebted to 

Ralph W. Imlay of the Paleontology and Stratigraphy Branch of 

the U.S. Geological Survey for his prompt identification of Jurassic 

and Cretaceous invertebrate fossils and to Roland W. Brown of the 

same organization for his identification of Tertiary plants. 

GEOMORPHOLOGY 

TOPOGRAPHY 

The Mount Katmai area is divided asymmetrically by the volcanic 

Aleutian Range. The mountains rise steeply from the fiordlike bays 

of the Shelikof Strait coastline to altitudes greater than 7,000 feet, 

and parallel the northeasterly trend of the peninsula across the 

entire area. From the crest of the mountain range the altitudes of 

the peaks drop less abruptly westward and northwestward, and beyond the limit of the area mapped the topography passes into a low 

coastal plain. 

A line of high mountain peaks, many of which are either dormant 

or active volcanoes, extends from Mount Douglas on the northeast to 

Martin Mountain on the southeast. Between these limits lie Fourpeaked Mountain, the relatively low Kaguyak Crater, and the cones 

of Kukak Volcano, Mount Denison (with an a:ltitude of 7,606 feet, 

the highest peak in the area mapped), Snowy Mountain, Mount Katmai, Trident Volcano, and Mount Mageik. Six miles northwest of 

Mount Katmai the cone of Knife Peak Volcano rises from the Valley 

of Ten Thousand Smokes to an altitude of 7,589 feet. 

Most of the range between Martin Mountain and Kukak Volcano 

is built of successive volcanic flows and generally exceeds 4,000 feet 

in altitude, except where headward-cutting streams locally have dissected it. Within these geographic limits Katmai Pass is the only 
GEOLOGICAL SURYEY BULLETIN 1058 PLATE 30 

tograp 

HALLO DAY GLACJEH SHOWING RECESSIONAL STAGE OF ICE 
GEOLOGICAL SURVEY 

FJOH.DLIKE BAYS OF SHELIKOF STH.AIT COASTLINE 

Geographic Harbor in foreground 

BULLETIN 1058 PLATE 31 

P hoto:;raph by U.S . Air Force 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 265 

low route through the mountains. Two passes have been cut through 

the volcanic rocks into sedimentary rocks of Jurassic and Cretaceous 

age northeast and southwest of this part of the range, one in the 

watershed area of Takayoto Creek and the Kejulik River and one 

southwest of Kaguyak Crater near the headwaters of the Savonoski 

River. 

The area underlain by the Naknek and Kaguyak formations, although mountainous, is less rugged than the area underlain by the 

volcanic rocks. Locally, glaciers have carved a fretted upland of 

aretes and cirques within this pa.rt of the map area, but between the 

Kamishak and the Douglas Rivers the upland comprises mesalike 

plateaus locally capped by resistant sandstone and conglomerate. 

A belt of hills along the northwest side of the mountains is underlain by intrusive rocks, and from this belt lower hills underlain by 

volcanic rocks merge westward with the subdued topography of the 

Bristol Bay coastal plain. 

DRAINAGE 

RIVERS 

The area is drained by four major rivers: the Savonoski, Ukak, 

Kamishak, and Katmai. These rivers predate the Pleistocene and 

probably were carved in an early Tertiary surface. The glaciers 

probably enlarged and straightened the previously established courses. 

During recession of the ice, glacial deposits cove.red the valley floors, 

and these deposits, which are being constantly reworked, form the 

flood plains of the rivers. 

The largest river in the map area, the Savonoski, heads in relict 

cirques and active glaciers of the Aleutian Range and flows through 

a glaciated valley about 5 miles wide. Within this valley many small 

streams interconnect to form a braided pattern; their channels total 

about one-fourth of the area of the river's flood plain. The gradient 

of the Savonoski averages 20 feet per mile between the Hook Glacier 

and the Rainbow River and less than 12 feet per mile between the 

Rainbow River and its confluence with the Ukak River. 

The Ukak River rises in the volcanic slopes of the Aleutian Range, 

and its tributaries, River Lethe and Knife Creek, drop about 100 feet 

per mile from the base of Baked Mountain through the Valley of 

Ten Thousand Smokes. From this valley the Ukak River drops 

about 50 feet per mile to its confluence with the Savonoski River, 

where the combined waters empty into Iliuk Arm. 

The Katmai River, which drains a relatively small part of the map 

area, heads in the volcanic spine of the Aleutian Range and flows 

493909-59-2 
266 MT.NERAL RESOURCES OF ALASKA 

southeastward to Shelikof Strait. The river flows transverse to the 

regional structure through a glaciated U-shaped valley about 5 miles 

wide. The floor of this valley is composed of thick ash deposits 

from the 1912 eruption of Mount Katmai, and the river, flowing on 

these deposits, comprises hundereds of small streams which interconnect to form a braided pattern. The gradient of the rive.r, except in 

its headwaters, averages 10 feet per mile. 

Unlike the Savonoski, Ukak, and Katmai Rivers, which flow transverse to structural trends, the Kamishak and smaller related drainages are subsequent streams. The Kamishak River, paralleling the 

northeastward-trending regional structure, heads in relict cirques 

and active glaciers of the volcanic mountains and sedimentary-rock 

uplands, flows northeastward, and, beyond the map area, receives the 

water of the little Kamishak River and empties into Akumwa.rvik 

Bay. On the upper 13 miles of the river the gradient averages 35 

feet per mile. Below its junction with the South Fork the gradient 

averages 18 feet per mile. 

LAKES 

In the northwest corner of the map area a group of interconnected 

lakes receives the water of most of the westward- and northwestwardflowing streams. West of the map area these lakes are drained by 

the Naknek River, which meanders through the lake-studded Bristol 

Bay coastal plain and empties into Kvichak Bay. The lakes are 

glacial in origin, and their beds were scoured in intrusive and volcanic rocks. They lie less than 200 feet above sea level. 

GLACIATION 

Fieldwork by the authors was concentrated mainly on the study of 

Mesozoic and Cenozoic stratigraphy and structure, and less so on the 

study of the glacial geology of the area. Mapping of the glacial features (see pl. 29) was based in part upon observations in the field, 

but for the most part resulted from interpretation of vertical aerial 

photographs. The authors interpret that at least two separate glaciations occurred, and that these correspond to the Brooks Lake and 

Iliuk Arm glaciations described by Muller (1953, p. 2-3) and assigned 

to late Wisconsin age by Pewe and others (1953, p. 13). 

In the northwestern part of the map area, terminal moraines of the 

two glaciations are clearly preserved (pl. 29). The older of these 

two, the Brooks Lake, is superimposed on what may be a partly obscured ground moraine of an earlier advance. The Brooks Lake advance is represented by a series of arcuate generally undissected lateral and terminal moraines enclosing Lake Brooks, Ida vain Lake, 

Lake Coville, and Hammersly Lake. Muller (1953, p. 2) reports that 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 267 

moraines of this advance also enclose N alrnek Lake. In addition, moraines in the Angle Creek area, and those bordering the south side of 

N anwhyenuk Lake and Kulik Lake, probably also are related to this 

ice advance. Areas enclosed by the lateral and terminal moraines are 

characterized by knob-and-kettle topography. Streams have breached 

the terminal moraine ridges only to a minor extent, and in general 

the glacial topography in the terminal zones completely controls the 

drainage pattern. For example, water from Hammersly Lake flows 

northward by way of American Creek to a point where it is blocked 

by the moraines that border N anwhyenuk Lake. From here it flows 

westward, and then, controlled by the arcuate trend of the moraine 

enclosing Lake Coville, it flows southward to join the Savonoski 

drainage. The water traverses an arc of almost 330° from the point 

at which it originates. 

The Iliuk Arm glaciation, considered by Muller (1953, p. 2-3) to 

be the youngest major advance in this area, is represented by the moraine enclosing Iliuk Arm. Probably also associated with this readvance are moraines forming the narrow neck of land between Lake 

Coville and Lake Grosvenor, and small push moraines on the north 

side of Lake Grosvenor (pl. 29). 

In addition to the area northwest of the mountains, the Shelikof 

Strait side probably underwent glaciation also. On this side of the 

map area, the Katmai River flows through a typical U-shaped glacial 

valley, and glacially scoured fiords typify the coastline :from Katmai 

Bay to Cape Nukshak. Fieldwork by the authors was not detailed 

enough for them to correlate the times of the glaciation here with the 

advances on the northwest side of the mountains, but it is reasonable 

to believe that glaciation on both sides was concurrent. 

Many active alpine glaciers are present in the area mapped. In 

the vicinity of Mount Douglas only the highest peaks stand above 

the level of the glacial ice and perennial snowfields, and, over much of 

the central part of the area, headward-cutting glaciers are carving a 

fretted upland of cols and aretes. Judging from the position of many 

of the glaciers with respect to their recently deposited end moraines, 

it appears that the ice is now receding (pl. 30). A glacier in the 

crater of Mount Katmai is of special interest, as noted by ]d:uller, 

Juhle, and Coulter (1954, p. 70). This crater originated during the 

eruption o:f Mount Katmai in 1912, and the glacier that now oecupies 

it is therefore one of the few in the world whose age can be accurately 

determined. 

COASTLINES 

The coastline along Shelikof Strait between Katmai Bay and Cape 

Nukshak (pl. 31) is characterized by deeply indented harbors, is-
268 MLNERAL RESOURCES OF ALASKA 

lands, and peninsulalike projections. The beaches along the coastline are poorly developed. The most pronounced beaches are at Rallo 

Bay, where older beach levels are now as much as 30 feet higher than 

the present high-tide level. Extensive beaches are not typical of the 

other bays in the area, and those at Rallo Bay may be caused by the 

development of beach features on a more extensive glacial outwash 

plain than is found elsewhere in the area mapped. 

RECENT VOLC~SM 

Active volcanoes were observed in this region as early as 1898, when 

Spurr (1900, p. 232), traversing the Katmai area, noted that: 

The summit of the Aleutian Mountains in this vicinity is formed by a continuous chain of volcanoes. One of these volcanoes is said by the natives to 

smoke occasionally. Earthquakes and hot springs are among the volcanic 

phenomena actually experienced in the region, and the continuation of the chain 

of volcanoes extends to those which have been active in historical time, such 

as St. Augustine and the volcano in the ytcinity of the Ugashik Lakes, as well 

as many others along the same range farther southwest. 

In June of 1912 the natives living at Savonoski and at Katmai were 

forced to abandon their villages because Mount Katmai, which had 

been nearly dormant, explosively erupted. R. F. Griggs (1922) has 

published a detailed account covering both this eruption and the 

emplacen1ent of the incandescent volcanic debris in the Valley of Ten 

Thousand Smokes. 

In addition to the eruption of Mount Katmai, other volcanic activity has been observed in this area in recent time. Muller, J uhle, 

and Coulter (1954, p. 62-64) report that 15 recently active volcanoes 

have been noted. Martin, Mageik, Novarupta, Knife, Kukak, and 

Douglas peaks were observed to steam with varying intensities during 

the summers of 1953 and 1954, and Trident Volcano was steaming and 

extruding a blocky viscous lava. 

STRATIGRAPHY 

UNDIFFERENTIATED ROCKS OLDER THAN MIDDLE JURASSIC 

The undifferentiated sedimentary and metamorphic rocks older 

than Middle Jurassic were not studied on the ground by the authors. 

The nature and distribution of this sequence have been inferred from 

the examination of vertical aerial photographs. The rocks are 

limited in their distribution to the vicinity of Kulik Lake where they 

crop out in resistant ridges and scarps. They appear to be bedded and 

composed of relatively massive units. With the present information 

they cannot be correlated with rocks of adjoining outcrop areas, but 

they appear to be intruded on their east side by an igneous complex 

of presumed Early and (or) Middle Jurassic age (see p. 287) and 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 269 

may be partly equivalent to the crystalline limestone schist and quartzite of Paleozoic(~) age mapped by Mather (1925, p. 163-164) at 

the head of the Paint River, or to the Paleozoic and early Mesozoic(~) 

age rocks exposed in the vicinity of Lake Iliamna (Martin and Katz, 

1912). 

BEDDED ROCKS OF MESOZOIC .AGE 

NAKNEK FORMATION 

History.-The name Naknek was given to a rock "series" by Spurr 

(1900, p. 170), who stated: 

The Naknek series consists of a great thickness series of granitic arkoses and of 

of conglomerates which generally contain pebbles of granite. 

He further noted (p. 169-170) that 

at Katmai Point the basal rock exposed just above tidew3.ter is hard massive 

grani~ic arkose; above this comes a dense aphanitic rock ... and higher up 

come arkoses, made up of very coarse granitic fragments, and coarse conglomerates, having pebbles of biotite granite. Through all the rocks of this series 

indistinct plant remains are common. 

On the basis of the available information it is not quite clear where 

the type locality of the Naknek was intended to be, nor is it entirely 

clear what Spurr considered the upper and lower limits. Presumably 

Spurr had no specific type locality in mind, but intended that the name 

represent the rocks exposed from Mount Katolinat to Katmai Pass, 

and southward to Katmai Bay. Martin (1905, p. 44) used the word 

formation in place of series, and the name Naknek formation as it 

is used now applies to a sequence of rocks of Late Jurassic age locally 

having a basal conglomerate member. Martin and Katz (1912) 

originally applied the name Chisik to this conglomerate and treated 

it as a unit of formational rank overlying the Chinitna shale and 

underlying the Naknek formation, but in 1926 Martin treated the 

Chisik conglomerate as the basal member of the Naknek formation, 

and this is its present usage. 

In 1925, Mather mapped a conglomerate unit as the Chisik conglomerate over the crest and along the flanks of the Kamishak anticline, and the authors have extended this mapping along part of the 

·shoreline of Lake Grosvenor (pl. 29) . The contact of this conglomerate unit with older rocks is not exposed in the m~p area, and its 

identification by Mather as the Chisik conglomerate apparently was 

based on the lithologic similarities of the conglomerate in the Mount 

Katmai area to the one described by :A1artin and Katz (1912) in the 

Iliamna region. 

Occurrence and lithology.-The Naknek formation crops out in a 

mountainous belt 20 to 38 miles wide which trends northeastward 
270 MIT.NERAL RESOURCES OF ALASKA 

across the entire area. On the northwest side of its outcrop belt the 

formation is in fault contact with igneous rocks of Early and (or) 

Middle Jurassic age. In the northeastern part of the map area it is 

overlain partly by rocks of Cretaceous age, and both here and over 

much of the central part of the map area it is overlain by volcanic 

rocks of Tertiary and Quaternary age. 

The Chisik conglomerate member consists of irregularly bedded 

marine conglomerate which, north of the mapped area, may be as 

much as 1,000 feet thick (Mather, 1925, p. 169). Along the northeast 

shore of Lake Grosvenor the conglomerate contains large generally 

rounded cobbles and boulders of granite, chert, jasper, and metamorphic and mafic igneous rocks in a green feldspathic fossiliferous 

sandstone matrix. The conglomerate is lenticular and is interbedded 

with coarse green arkose. The thickness of the member undoubtedly 

varies considerably throughout the area, and its contact with the 

overlying beds of theN aknek formation is gradational. 

The part of the Naknek formation above the Chisik conglomerate 

member consists of 6,000 to 9,000 feet of marine sandstone, siltstone, 

conglomerate, and shale. The lowest 800 feet of this sequence is composed of fine- to coarse-grained arkose of low to medium porosity and 

low permeability. The sandstone contains rounded fragments of 

gray and green chert, feldspar, and white quartz, with interbedded 

dense medium-gray siltstone and sandy red-weathering shale. Thin 

beds and lenses of conglomerate containing granite, chert, and metamorphic and mafic igneous detritus in a feldspathic green argillaceous 

matrix are present, and limy and nonlimy siltstone concretions and 

carbonaceous material occur sporadically. The 800 feet is fossiliferous, and specimens of Aucella, which is the predominant fossil 

type, are so abundant that locally the rock is coquinoid. 

Overlying the lowest 800 feet is about 2,000 feet of less resistant 

predominantly thin-bedded siltstone, fine-grained sandstone, and 

sandy shale. Conglomerate similar to that described above occurs as 

minor lenses. The Aucella sp. which characterizes the lower beds is 

present to a lesser degree in this part of the sequence. 

The upper 3,000 to 6,000 feet of the Naknek formation consists 

locally of massive conglomerate, similar in composition to the basal 

Chisik conglomerate member, interbedded with fine- to coarse-grained 

fossiliferous arkose, siltstone, and shale. Massive conglomerate units 

as much as 2,000 feet thick and composed predominantly of large 

boulders of silicic and mafic intrusive rocks in a green fossiliferous 

sandstone matrix crop out at Mount Katolinat. Pebbles of biotite 

granite are abundant throughout the rocks in the upper 3,000 to 6,000 

feet of the formation, and as Spurr (1900, p. 170) notes, many of 

the upper beds contain macerated plant remains. 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 271 

Measured stratigraphic sections.-Only one section which was incomplete, was measured by the authors in the field. This section is 

on the northeast side of Lake Grosvenor (pl. 29) where the essentially 

flat lying beds of the Naknek formation crop out in resistant benches. 

Neither the upper nor the lower contact of the formation is exposed. 

Units of this stratigraphic section (1, pl. 32) are described below in 

descending succession. 

Section 1: Naknek formation on northeast side of Lake Grosveno1 

[Location, pl. 29; graphic section, pl. 32] Thickness 

(feet) 

1. Siltstone, sandstone, and shale. Upper beds consist of gray highly 

indurated massive siliceous siltstone, and gray-green sandstone; 

remainder of unit consists of gray-green fossiliferous sandstone, 

gray dense slabby siltstone, and red-weathering sandy shale. 

Partly covered________________________________________________ 840 

2. Siltstone, gray, resistant, dense, makes up large part of unit; minor 

interbedded fine-grained arkose of low porosity and permeability. 

Aucella sp. common throughout. Partly covered________________ 600 

3. Sandstone, gray-green, fine-grained, subgraywacke-type, with 

granules of green and gray chert, and jasper ; and gray dense platy 

siltstone. A ucella sp. rare_____________________________________ 140 

4. Arkose, light-gray to green, fine-grained, Aucella-bearing__________ 60 

5. Sandstone, light-gray to green, slabby, argillaceous, and gray interbedded siltstone. Aucella sp. common___________________________ 75 

6. Siltstone, green, grades to green sandstone; minor thin carbonaceous 

seams. Aucella sp. common____________________________________ 125 

7. Siltstone, gray, dense, well-indurated, noncalcareous; in %- to 2-

inch beds, abundantly fossiliferous. Fossil colin. 25277, near top 

of unit------------------------------------------------------- 300 

8. Sandstone, green, fairly well sorted, locally coquinoid, fossiliferous. 

Fossil colln. 25276--------------------------------------------- 50 

9. Sandstone, green-gray, coarse-grained, noncalcareous. Detrital constituents are well rounded fairly well sorted green and gray chert 

and feldspar, and white quartz. Aucella sp. and pectinoid pelecypods abundant------------------------------------------------ 90 

10. Siltstone, gray, massive; contains lenses of conglomeratic sandstone 

with subrounded chert grains in a green fossiliferous sandstone 

matrix ; grades into Chisik conglomerate member below. Interval 

abundantly fossiliferous; fossil conn. 25278______________________ 80 

11. Conglomerate, marine, with large well-rounded cobbles of granite, 

chert, and mafic igneous rock in a green fossiliferous matrix; 

makes up Chisik conglomerate member. A ucella sp. common____ 80 

Total measured Naknek formation _______________________ 2, 440 

Age and correlation.-J urassic fossils collected by the authors are 

listed below. Identifications are by R. W. Imlay, of the U.S. Geological Survey. In the first colmnn in this table and other tables of 

fossils that follow, "USGS Mesozoic loc." refers to the Geological 
272 MINERAL RESOURCES OF ALASKA 

Survey Mesozoic locality number under which the fossils are 

filed. Fossil collections 25276, 25277, and 25278 were obtained from 

stratigraphic section 1 at Lake Grosvenor (pis. 29 and 32). Lot 

25279 was collected from an isolated cutbank on the south side of 

Lake Grosvenor (pl. 29) . 

USGS 

Mesozoic Zoe. I dentijication 

25276 A ucella rugosa (Fischer) 

Aucella mosquensis (von 

Buch) 

M eleagrinella sp. 

25277 A ucella rugosa (Fischer) 

Aucella mosquensis (von 

Buch) 

USGS 

Mesozoic Zoe. Idenifijication 

25278 .Aucella mosquensis (von 

Buch) 

A ucella rugosa (Fischer) 

Pleuromya sp. 

25279 Aucella mosquensis (von 

Buch) 

Pleuromya sp. Rhynchonellid brachiopods 

Smith (1925, p. 199-200) made several fossil collections in the 

southwest part of the area mapped by the authors. The localities 

are plotted on plate 29, but, owing to the difference in the base maps 

used by Smith and by the authors, the positions may not be exact. 

Smith ( 1925, p. 200) lists the following fossils identified by T. 'V. 

Stanton: 

12077. East side of Kejulik Pass, below Gas Creek: 

Rhynchonella sp. 

Pleuromya sp. 

Turbo? sp. 

Belemnites sp. 

Phylloceras sp. 

Bone fragment 

Jurassic, Naknek 

12078. Upper part of Gas Creek. Lowest exposed beds: 

Aucella sp. 

Eumicrotis sp. 

Jurassic, Naknek 

12079. Mountain top east of Yori Pass: 

.Aucella mosquensis (von Buch) 

Astarte sp. 

Pleuromya sp. 

Jurassic, Naknek 

12080. Baked Mountain, north side of Valley of Ten Thousand Smokes: 

.Aucella mosquensis (von Buch) 

Lima sp. 

Turbo? sp. 

Belemnites sp. 

Jurassic, Naknek 

Rocks of the Naknek formation are wid.espread on the Alaska 

Peninsula as· well as in other areas including the Matanuska Valley 

and Talkeetna Mountains. Imlay ( 1952, p. 977-978) points out that 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 273 

The basal part of the Naknek formation is of lower Oxfordian age ( mariae to 

plicatilis zones of northwest Europe) , as ·Bhown by the presence of various 

species of Oardioceras in the Cook Inlet area .... [and] in the Matanuska 

Valley. . . . The overlying beds in the lower part of the Naknek formation are 

of . probable upper Oxfordian age, as shown by the presence of Amoeboceras 

(Prionodoceras) associated with finely striate Aucella bronni (Rouiller) ... 

A Kimmeridgian age to basal Portlandian age for the upper part of the Naknek 

formation is shown by the presence of Aucella mosquensis (von Buch) and 

A .. rugosa (Fischer) • • • 

A ucella bronni has been more recently designated aucella concentrica. 

In the Mount Katmai area the Oardioceras zone and the Amoeboeeras zone are not represented in the lots collected by the authors. 

Aucella rugosa and Aucella mosquensis, which Imlay believes are 

characteristic of the Middle Kimmeridgian to Lower Portlandian 

stages (see fig. 45), occur in beds that are not more than 80 feet 

above the upper contact of the Chisik eonglomerate member. Unless 

the Chisik, as mapped by the authors, is representative of Imlay's 

two older zones, it would appear that there are overlap relationships 

within the Naknek formation. Another alternative is possible, however. It has already been noted that the assignment of this conglomerate member to the Chisik was done by Mather (1925), and 

that the assignment was apparently based on lithologic similarities 

of the conglomerate in the Mount Katmai area to that described by 

Martin and Katz (1912) in the Iliamna region. The authors recognize little lithologic difference between the conglomerate unit that 

has been mapped as Chisik in the Mount Katmai area and other conglomerate units that are higher in the Naknek formation, and, although they have retained Mather's mapping, they believe it possible 

·that the conglomerate mapped as Chisik in the Mount Katmai area 

is younger than, and may not be continuous with, the type Chisik. 

KAGUYAK FORMATION 

History.-The name Kaguyak formation is proposed herein to 

designate the sequence of rocks of Late Cretaceous age that is typified by the stratigraphic section exposed in the vicinity of Kaguyak. 

The type section includes the exposures at Kaguyak and the sequence 

exposed in the sea cliffs from the mouth of the Big River to the 

Swikshak River. Atwood (1911, p. 41) included these rocks as part 

of the Chignik formation. However, as this section has relatively 

little in common with the coal-bearing sequence at Chignik, about 

250 miles to the southwest, it seems more logical to assign a different 

formation name to the Upper Cretaceous beds in this area. 

Other geologists have studied the rocks in this .vicinity in the past~ 

Martin (1926, p. 299) states: 

493909-.,..59-----3 
274 MHfERAL · RESOURCES OF ALASKA 

The north shore of Kaguyak Bay, near Aievak or Douglas Village, not 

far from the east end of the Alaska Peninsula, contains an almost unbroken 

series of outcrops of sedimentary rocks striking slightly north of west and 

Quaternary 

Tertiary 

Cretaceous 

Jurassic 

Series 

Pliocene 

European 

Volcanic · flows 

FIGURE 45.-Correlation chart of formations in the Mount -K'8.6nai area,::· 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 275 

dippirig 15° N. The westernmost exposures consist of dark shale with marine 

Upper Cretaceous fossils . . , The rocks in the east end of tbe cliffs consist of 

gray sandstone with thinner beds of dark shale in which no fossils were found, except fragmentary dicotyledonous leaves that were too imperfect for identification. 

Hazzard ( 1950) reports as follows concerning the exposures on the 

Kaguyak promontory: 

About 400 feet of beds comprising fossiliferous, concretionary, black 

limy siltstone with thin beds of dark bluish-gray limestone are exposed in the 

sea cliffs on the cape and in the surrounding reefs. The presumed base of the 

Cretaceous is in a 30-foot greenish-gray fine-grained sandstone cropping out at 

the mainland edge of the sandflat west of the cape. The nature of the intervening section is unknown. The basal sandstone rests with apparent conformity on the Upper Jurassic Naknek formation. 

The 30-foot-thick sandstone bed described by Hazzard is considered 

by the authors to represent the lower limit of the Kaguyak formation 

in this area. The upper beds of the formation are overlain by volcanic rocks of Tertiary age of the Aleutian Range. 

Occurrence and lithology.-The Kaguyak formation is confined in 

its geographic distribution to the . northeastern part of the mapped 

area. Only the exposures in the vicinity of Kaguyak were visited 

by the authors, and the extension of the formation elsewhere in 

the area is based largely on the interpretation of vertical aerial 

photographs. 

The formation has been divided into three informal members: a 

lower fossiliferous siltstone member, a middle massive locally crossbedded concretionary sandstone and interbedded siltstone and silty 

shale ·member, and an upper thin-bedded sandstone and siltstone 

member. In the exposures at the type locality the lower member is 

about 2,000 feet thick, the middle member is 1,090 feet thick, and the 

upper member is about 1,460 feet thick. The upper contact of the 

formation was not seen. 

Type section.-Units of the type section (2, pis. 29 and 32) are 

described below in descending stratigraphic succession. 

Section 2: Type section of the Kaguyak formation at Kayuyak along the sea 

cliffs from Big River to Swikshak River. 

[Location, pl. 29 ;, graphic section, pl. 3·2] 

Thickne8B 

(feet) 

1. Sandstone and silt shale, gray, interbedded, very fine grained to finegrained, argillaceous, noncalcareous, red-weathering; sandstone 

locally contains carbonaceous partings and minor ironstone______ 760 

2. Sandstone, ironstone, and silt shale ; platy and rusty-weathering; 

sandstone ls fine grained. Interval largely covered--------------- 700 

3. Sandstone, siltstone, and silt shale, interbedded, light-gray, finegrained ; sandstone in beds as much as 4 feet thick, with thinner 

interbeds of siltstone and silt shale--------------------------- 75 
276 MINERAL RESOURCES OF ALASKA 

TAicknu.t 

(feet) 

4. Silt shale, predominantly; l-inch interbeds· of· sandy siltstone and 

silty sandstone ; limy dense spheroidal siltstone concretions 

conunon------------------------------------------------------- 75 

5. Sandstone, light-. to medium-gray, fine- to medium-grained, massive, 

shale interbeds 1 foot thick____________________________________ 55 

(i. Sandstone, gray, medium-grained, massive, .slightly, argJIIt~c~f.n.J~.· 

Large spheroidal sandstone concretionS------------------------ 50 

1. Sandstone, light-gray, fine-grained, massively bedded; with siltstone 

concretions alined on bedding planes ; black silt shale at base of 

uni~-------------------------------------------------------- 80 

8. Sandstone, siltstone, and silt shale; rhythmically bedded. Sandstone is light gray, fine- to medium-grained, with shaly partings 

and large spheroidal siltstone concretions locally alined on bedding 

surfaces; silt shale is dark gray, with platy to hackly fracturing; 

sandstone units up to 6 feet thick ; siltstone and silt shale units up 

to about 8 feet thick; interbeds in shale unit several inches thick__ 250 

9. Silt shale, siltstone, and sandstone. Rhythmically bedded unit of 

dark-gray well-indurated silt shale, dense noncalcareous hackly 

fracturing siltstone, and light-gray fine-grained well-indurated noncalcareous sandstone. Sandstone contains shaly partings and clay 

galls, and is found in beds 2 inches to 10 feet thick, with thinner 

interbeds of siltstone and silt shale. Large spheroidal siltstone 

and sandstone concretions locally alined on bedding surfaces____ 205 

10. Sandstone, silt shale, and siltstone. Sporadic outcrops of light reddish-weathering fine-grained sandstone, medium-gray platy silt 

shale, and dense siltstone; shale galls. Partly covered_________ 300 

11. Andesite sill. Petrographic description (sample 54 AKe 45) : Megascopically a medium-dark-gray phaneritic rock. Microscopically 

holocrystalline and· equigranular. · It consists predominantly of 

unoriented interfingering laths of plagioclase averaging 0.25 mm 

in length ; interstices between the plagioclase laths filled with 

grains of augite. The plagioclase is predominantly andesine; the 

augite is in part altered to amphibole. Grains of pyrite are also 

present------------------------------------------------------- 40 

12. Covered interval------------------------------------------------ 220 

13. Siltstone, dark-gray, hackly fracturing, dense, noncalcareous, with 

calcite veining along distinct joint system ; large spheroidal limy 

dark-gray fossiliferous siltstone concretions alined on bedding 

planes have a fetid odor on fresh break. Entire section fossil 

bearing; fossil colln. 25282 and 25283-------------------------- 490 

14. Covered interval------------------------------------------------ 230 

15. Siltstone, medium-gray, very dense, massively bedded, siliceous, 

breaks down in needlelike fragments and hackly fracturing silt 

shale. Abundant large spheroidal limy dense siltstone concretions, 

locally pyritized and abundantly fossiliferous, alined on bedding 

planes. Section near base becomes slightly sandy. Fossil colin. 

25280 and 25281_---------------------------------------------- 720 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 277 

Thickrness 

(feet) 

16. Covered interval. Projection of strike across to Kaguyak indicates 

that not more than 300 feet of additional section is present between unit 15 and the contact at Kaguyak described by Hazzard 

(1950, p. 227) ---------------------------------:---------------- 300 

Total measured Kaguyak forn:•ation ______________________ . 4, 550 

Naknek formation. 

Age and eorrelation.-Fossils collected from the lower siltstone 

member of the Kaguyak.formation were identified by Imlay. These 

samples were collected from stratigraphic section 1, the location of 

which is shown on plate 29. The positions of the collections in the 

stratigraphic column are shown on plate 32. 

UBGB 

Mesozoic Zoe. Identification 

25280 Inoceramus sp. 

Pleuromya sp. 

25281 Pachydiscus (N eodesmoceras) 

sp. 

Inoceramus cf. I. kusiroensis 

Nagao and Matumoto 

Nemodon sp. 

UBGB M«~s~oic Zoe. Identification 

Anomia cf. A. vancouverensis 

Gabb 

25282 Lytoceras ( Gaudryceras) sp. 

25283 Inoceramus cf. I. kusiroensis 

Nagao and Matumoto 

Inoceramus cf. I. shikotanensis Nagao and Matumoto 

Concerning these collections, Imlay ( 1954, written communication) 

states: 

The fossils from the Kaguyak formation are of Campanian or Maestrichtian 

age and are younger than any fossils found in the Chignik formation in the 

southern part of the Alaska Peninsula. In the Talkeetna Mountains fossils 

identical with those in the Kaguyak formation occur at the top of the siltstone 

member of the Matanuska formation just bE~low the highest sandstone member. 

The smooth compressed pachydiscid ammonite from fossil lot 25281 is good evidence of a position high in the Upper CrE~taceous sequence. The small Inoceramus with sharp, equally-spaced ribbing that is c9mpared with I. kusiroensis 

Nagao and Matumoto is likewise common in the high Cretaceous beds. 

In addition to the collections made by the authors at this locality, 

fossils of Late Cretaceous age are known also to occur in the upper 

beds that form the hills between the ICamishak and Douglas Rivers. 

Imlay and Reeside (1954, p. 234) state: 

Ammonites of Late Cretaceous age, probably Campanian, have ~n found at 

Cape Kaguyak on the Shelikof Strait in the upper part of a sequence consisting 

of about 400 feet of black siltstone and thin beds of limestone overlying the 

Naknek formation (Hazzard 1950, p. 227). 'rhe ammonites include Pachydi8cu8 

cf. P. ootacodensis Stoliczka, P. suciaem·is (Meek), PhyZloceras ramosum 

(Meek), Gaudryceras cf. G. denmanense Whiteaves, and Diplomoceras notabile 

Whiteaves. With these is one specimen of Inoceramus that is probably an im· 
278 M~ERAL RESOURCES OF ALASKA 

mature form of I. subundatus (Meek). The same assemblage has been found. 

also, about 7 miles southeast of the mouth of the Kamishak River. 

BEDDED ROCKS OF CENOZOIC AGE 

COA~BEARING ROCKS 

History.-The term coal-bearing rocks is here used to designate the 

coal-bearing rocks of Tertiary age that are exposed in the Katmai 

area. Coal-bearing rocks on the Alaska Peninsula were mentioned 

by Dall and H~rris (1892, p. 238), who stated that 

along the shores of Alaska Peninsula, west and south from Cook's Inlet, lignite 

beds, doubtless associated with plant impressions, are not uncommon, but the 

exploration of this shore has been very imperfect. 

Atwood (1911, p. 49-51) described coal-bearing rocks of Tertiary age 

at Cape Douglas and between "Rallo Bay and Amalik." 

Coal-bearing sedimentary rocks were said by Smith (1939, p. 62) 

to be found in patches all the way from Cape Douglas to and beyond 

Pavlof Bay. 

Occurrence and lithology.-The coal-bearing rocks crop out on the 

northward-facing fault scarp along the south side of Rallo Bay, at 

Dakavak Lake, and at Geographic Harbor. These rocks probably 

are also present on the south side of Katmai Canyon, and judging 

from a sketch map by Stone (in Atwood, 1911, p. 50) they may be 

present also in the vicinity of Cape Douglas. They locally interfinger 

with volcanic rocks of Eocene age and cannot be mapped throughout 

the area. 

The Unit consists predominantly of nonmarine conglomerate, sandstone, siltstone, coal, and plant-bearing mudstone, and ranges from 

rocks deposited in lagoons or swamps to those deposited on the Eocene 

beaches. Volcanic rocks are locally interbedded. 

Conglomerate units of the coal-bearing rocks are up to 50 feet thick 

and contain pebbles, cobbles, and boulders of mafic igneous rocks~ 

granite, chert, silicified wood, and silicified tuff in a light-gray to 

green coarse-grained tuffaceous matrix. The fine- to coarse-grained 

light-gray sandstone units consist of chert, white quartz, granite, and 

mafic igneous detritus. Disseminated carbonaceous material and 

plant impressions are common. The sa.ndstone units are in general 

moderately porous and permeable. The sequence is further characterized by thin seams of lignite and low-rank coal, associated with plantbearing light-gray mudstone. . 

. M easurred stratigraphic secti()'flS.-Two stratigraphic sections of the 

coal-bearing rocks were measured in the field, one at Geographic 

Harbor ( 4, pls. 29 and 32) and one at Cape N ukshak ( 3, pls. 29 and 

82). The one at Cape Nukshak, the more complete of the two, is 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 279 

exposed on the northward-facing fault scarp that forms the divide 

between Kukak and Rallo Bays. The measured sequence dips 26° S. 

Neither the top nor the bottom contact of the unit was observed at 

this locality, but on the hillside facing Kukak Bay volcanic rocks 

crop out not more than 500 feet stratigraphically higher than the top 

beds of the measured section. Units of the Cape Nukshak section are 

described below in descending stratigraphic succession. 

Section 3: Goal-bearing rocks at Gape Nukshak 

[Location, pl. 29; graphic section, pl. 32] Thickness 

(feet) 

i. Sandstone and conglomerate; sandstone is light gray, fine to coarse 

grained, quartzose; conglomerate contains pebbles, cobbles, and 

boulders of white quartz, mafic and silicic igneous rocks, chert, 

and wood fragments. Thin seams of carbonaceous material, lignite, and plant-bearing claystone-------------------------------- 200 

2. Sandstone, fine-, medium-, and coarse-grained, quartzose; and conglomerate containing very well rounded pebbles of white quartz 

and black chert. Thin seams of lignite and carbonaceous material. 

Claystone with abundant leaf impressions. Colln. 54 AKe 36____ 100 

3. Conglomerate with coarse-grained tuffaceous matrix; massive, containing pebbles, cobbles, and boulders of mafic and silicic igneous 

rocks, chert, and white quartz_________________________________ 40 

4. Sandstone, light-gray to green, fine-grained, massive quartzose, containing carbonaceous wood impressions ; and interbedded greengray leaf-bearing siltstone______________________________________ 50 

5. Sandstone, light-gray, fine- to coarse-grained, locally carbonaceous, 

moderately porous and permeable; and conglomerate containing 

pebbles of black chert, white quartz, granite, and mafic igneous 

rocks. Top of unit consists of lenses and beds 1 foot thick of carbonaceous material and lignite containing gray plant-bearing claystone. CoHn. 54 AKe 35---------------------------------------- 120 

6. Sandstone, greenish-gray, coarse-grained, friable, slabby weathering. 

Detrital constituents are predominantly quartz and minor black 

chert --------------------------------------------------------- 30 

7. Conglomerate with light-gray tuffaceous matrix, massive; contains 

pebbles and cobbles, as much as 8 inches in diameter, consisting of 

mafic igneous rock, granite, white quartz, silicified wood, black 

chert, green chert, and silicified tuff_____________________________ 50 

8. Sandstone, light-gray, coarse- to fine-grained, locally carbonaceous ; 

beds 2 inches thick-------------------------------------------- 50 

9. Conglomerate, massive, contains pebbles and cobbles of silicic and 

mafic igneous rock as much as 8 inches in diameter; carbonaceous 

matrix ------------------------------------------------------- 25 

10. Sandstone and conglomerate, interbedded------------------------- 20 

11. Conglomerate, massive; contains pebbles, cobbles, and boulders of 

mafic igneous rock, granite, chert, and silicified wood ; constituents 

mostly well rounded ; carbonaceous sandstone interbeds__________ 25 

12. Sandstone, coarse, pebbly, crossbedded; contains large lenses of lignite and coaly wood and lamellae of carbonaceous materiaL_______ 35 
280 MINERAL RESOURCES OF ALASKA 

Thicknue 

(feet) 

13. Siltstone, sandstone, and conglomerate. Siltstone is coaly, in l-inch 

beds interbedded with fine- to coarse-grained sandstone, and chertand quartz-bearing conglomerate________________________________ 45 

14. Sandstone, medium-gray, coarse-grained, pebbly-------------------- 40 

Total measured coal-bearing rocks at Cape Nukshak__________ 830 

The rocks exposed in the 280-foot incomplete stratigraphic section 

at Geographic Harbor (4, pis. 29 and 32), crop out along the southwest shore of Geographic Harbor and form the south flank of a 

northeastward-plunging·anticline. Units of the section are described 

below in descending stratigraphic succession. 

Section 4: Ooal-bearing rocks at Geographic Harbor 

[Location, pl. 29; graphic section, pl. 32]1 

Thickness 

(feet) 

1. Sandstone, platY------------------------------------------------- 12 

2. Sandstone, gray, friable, crossbedded, with conglomerate lenses____ 19 

8. Sandstone, coarse to conglomeratic, carbonaceous, with pebbles of 

white quartz, and mafic and silicic rocks________________________ 7 

4. Volcanic :flow rock, with interbedded carbonaceous material. Petrographic description of the :flow (sample 54 AKe 17) : Megascopically a medium-gray aphanitic porphyritic extrusive rock. The 

phenocrysts are white and average about 1 mm in length. Microscopically the rock is identified as sodic andesite. The microlites 

of plagioclase have the approximate composition AI4o. The laths 

of plagioclase are oriented in subparallel flow lines. Phenocrysts 

of former plagioclase and ferromagnesian minerals are completely 

replaced by calcite. Contains finely disseminated limonite and a 

large opaque inclusion of carbonaceous ( ?) materiaL_____________ 9 

5. Sandstone, medium-gray, coarse-grained__________________________ 6 

6. Sandstone, light-gray-green, fine-grained, massive; interbedded with 

shale ; plant bearing mudstone, and thin coal seams. Conn. 54 

Alre 16------------------------------------------------------- 15 

7. Basalt sill(?). Petrographic description (sample 54 AKe 15): 

Megascopically a dark dense aphanitic rock. Microscopically an 

intergranular holocrystalline rock. Plagioclase, predominantly 

labradorite, occurs as unoriented interfingering laths. Between 

the laths of plagioclase the interstitial augite(?) has altered to 

chlorite. Contains calcite, which probably represents an alteration product-------------------------------------------------- 13 

8. Siltstone-------------------------------------------------------- 3 

9. Shale, dark-gray; plant fragments common_______________________ 5 

10. Sandstone, dark-gray, crossbedded; with shale_____________________ 4 

11. Sandstone, dark-gray, dense, fine-grained-------------------------- 8 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 281 

Thickn.u#l 

(feet) 

12. Sodic andesite flow. Petrographic description (sample 54 AKe 14) : 

Megascopically a vesicular light-gray-green rock with some of the 

vesicles filled with quartz or calcite. Microscopically the rock is 

holocrystalline. The groundmass consists of lath-shaped microlites 

in a felty textured arrangement. The plagioclase has the approximate composition Ang0 (oligoclase-andesine). A few phenocrysts 

( 0.5 to 1.0 mm diameter) of calcic plagioclase are present. The 

specimen is highly chloritized and the chlorite probably is an alteration product of former ferromagnesian minerals. Secondary 

quartz is abundant-------------------------------------------- 5 

13. Sandstone and black silt shale, interbedded; nonlimy siltstone concretions------------------------------------------------------- 5 

14. Siltstone and carbonaceous shale, interbedded_____________________ 4 

15. Covered interval------------------------------------------------ 50 

16. Sandstone, interbedded, with platy, thin-bedded siltstone___________ 6 

17. Sandstone, light- to medium-gray, fine- to coarse-grained, massive, 

with abundant wood and carbonaceous materiaL________________ 18 

18. Shale, black, with abundant leaf impressions. Colln. 54 AKe 13______ 18 

19. Sandstone, very light gray, dense, salt-and-pepper textured; massive 

unit; conglomerate lenses containing wood fragments near base__ 62 

20. Coal and platy carbonaceous shale, interbedded------------------- 4 

21. Sandstone, friable, crossbedded__________________________________ 2 

22. Coaly shale----------------------------------------------------- 2 

23. Sandstone, light-gray, very fine grained, friable-------------------- 4 

24. Coal and silty sandstone, interbedded----------------------------- 2 

Total measured coal-bearing rocks at Geographic Harbor--- 280 

Age and correlation.:-Tertiary coal-bearing rocks of the Alaska 

Peninsula have been mentioned by many workers. Dall and Harris 

( 1892, p. 234-249) mentioned lignite beds along the shores of the 

Alaska Peninsula and discussed them as part of the "Miocene of the 

Kenai group." Atwood (1911, p. 49) stated that "Cape Douglas, the 

northeastern extremity of the peninsula, is composed in part of Tertiary rocks, presumably of Kenai age." Fossil evidence cited by Atwood indicates that the rocks he describes are of Eocene age. 

Smith (1939, p. 62-63), in speaking of coal-bearing Tertiary beds 

in southwestern Alaska, notes that they 

have been found in more or less discontinuous patches all the way from Cape 

Douglas * * * to and beyond Pavlof Bay * * *. Throughout this tract the 

lowest sedimentary beds appear to be in general closely comparable with the 

typical Kenai formation. 

Since 1928 the name Kenai formation has been used only for Eocene 

rocks of the Kenai Peninsula. However, the coal-bearing rocks of 
282 MINERAL RESOURCES-OF ALASKA 

rrertiary age that are described in this report may be comparable with 

the Kenai formation of Eocene age. -

The plant fossils collected from the formation by the authors were 

identified by Roland W. Brown. Collections 54 AKe 13 and 54 AKe 

16 were obtained at Geographic Harbor (4, pis. 29 and 32). Collections 54 AKe 35 and 54 AKe 36 were obtained at Cape N ukshak ( 3, 

pls. 29 and 32). 

FossiZ collection Identification· , _54 AKe 13 Glyptostrobus dakotensis (Brown) ; dicotyledonous leaves resembling Alnus, Betula, and Oorylus. 

54 AKe 16 ?Magnolia sp. 

54 AKe 35 Metasequoia occidentalis (Newberry) Chaney 

Alnus alaskana (Newberry) 

54 AKe 36 Metasequoia occidentalis (Newberry) Chaney 

Alnus alaskana (Newberry) 

Roland W. Brown (1954, written communication) states .that although the 1naterial from the first two localities is fragmental, there 

seems to be enough to suggest early Tertiary age. He further states 

that "The last two localities are definitely Tertiary, probably Eocene." 

In addition to the collections made by the authors at Cape N ukshak, 

collections were made at this locality by members of the Harriman 

Alaska Expedition of 1899. These excellent collections are listed by 

Atwood (1911, p. 52-54), who also quotes F. H. Knowlton's identification of them. Knowlton referred the collection to the upper Eocene. 

VOLCANIC FLOWS AND ASSOCIATED ROCKS 

Owing to the short time available for field studies, the authors made 

only a few observations of the volcanic flows and associated rocks in 

the area. Nevertheless, certain relationships, of the volcanic sequence 

are evident. Volcanism began at least as early as Eocene time and 

continued intermittently through the Tertiary and Quaternary 

periods. In addition, the volcanic-rock sequence includes a folded 

unit at least, in part, of Eocene age unconformably underlying 

younger undeformed flows. Because of the limited fieldwork it was 

not feasible for the authors to map this subdivision consistently, nor 

was it possible to determine the ages of all the intervals of volcanism. 

On the geologic map (pl. 29) the volcanic rocks have been subdivided 

into three units: a folded sequence, partly of Eocene age, which loGally 

contains nonmarine sedimentary members; a younger generally massive undeformed sequence; and an undifferentiated sequence comprising both. In addition, the undifferentiated unit locally comprises 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 283 

Kenai formation equivalents and Tertiary intrusive rock. The tdtal 

thickness of the volcanic rocks is probably more than 6,000 feet. 

The folded volcanic-rock sequence comprises interbedded andesjte, 

basalt, and water-laid tuff with local lenses of agglomerate, sa~dstone, siltstone, and plant-bearing mudstone. In the northwestern 

part of the area the sequence is composed of several thousand fee~ of 

these rocks, which locally overlie rocks older than Middle Jura~sic 

and Lower and (or) Middle Jurassic intrusive rocks. The volcapic 

sequence was deposited under much the same environmental conditions 

as its partial time equivalent, the coal-bearing rocks. The sediment*'ry 

lenses and interbeds of agglomerate consist of a volcanic maftix 

enclosing boulders of igneous rock and silicified wood. The igne~us 

detritus is predominantly mafic in composition, although pebbles! of 

granite occur locally. Interbedded in the volcanic rocks are mudflows, lenticular crossbedded coarse-grained green sandstone, tHinbedded to fissile coaly shale, and dense siltstone. Much carbonacepus 

material and many poorly preserved leaf impressions further ch!aracterize the formation. Fragments of leaves in one of the plant 

collections (54 ARr 1, Lake Grosvenor locality, pl. 29) were identified 

by Roland W. Brown (written communication) as belonging! to 

Metasequoia occidental is (Newberry) Chaney, 0 eroidiphyllum elliftioum (Newberry) Brown, and other dicotyledonous species. He st~tes 

that, although the material was fragmental, there appeared to1 be 

enough to suggest an early Tertiary age assignment for the sequence 

characterized by this flora. , 

Other folded volcanic rocks, consisting predominantly of interbedded flows, are exposed along the Shelikof Strait coastline betw~en 

Katmai Bay and Cape Nukshak, and may be present also from Cape 

Nukshak to the Douglas River. In the vicinity of Kukak Bay 1,960 

feet of layered volcanic rocks dip very gently northward (str~tigraphic section 5, pl. 29). The age of this sequence is unknown,, although the fact that it is folded suggests that it was deposited be:f~re 

Quaternary time, and the authors believe that it is probably E~ne 

in age. Twelve samples were collected from this section. The ba~alt 

and andesite flows have been hydrothermally altered, and the samples 

collected from near the base of this measured section appear to h~ve 

undergone the greatest alteration .. Individual flows are generally ~ess 

than 20 feet thick. Petrographic descriptions of the samples foll9w. 

The ~e~urem.en~, in feet are the stratigraphic position of the sample 

.above the base of the measured section. 
284 MLNERAL RESOURCES OF ALASKA 

Section 5: Layered volcanic rocks in the vicinity of Kukoik Bay 

[Location, pl. 29] Height 

above base oJ 

sectiorn 

(feet) 

Volcanic flow rock. Petrographic description (sample 54 AKe 22) : Megascopically a medium-gray aphanitic rock, containing abundant feldspar 

phenocrysts. In thin section the groundmass is seen to consist of a dense 

felty textured mass of microlites, cryptocrystalline quartz, and magnetite dust. Phenocrysts of partly altered plagioclase (including oligoclase and labradorite), averaging about 1.5 mm in length, are abundant. 

The ferromagnesian minerals are almost entirely replaced by chlorite, 

calcite, and talc(?). The groundmass is partly chloritized, and limonite staining is prevalent------------------------------------------- 1,960 

Basalt. Petrographic description (sample 54 AKe 23) : Megascopically a 

dense aphanitic brownish-gray rock. In thin section the rock seems 

to be equigranular and holocrystalline. The laths of plagioclase average 0.15 mm in length, are interfingering, and display a felty texture. 

In some areas of the slide a tendency toward subparallel flow-line orientation is apparent. Extinction angles indicate that the plagioclase 

has the approximate composition Anao (labradorite). The interstices 

are filled with augite grains in various stages of alteration. Larger 

grains, 0.4 mm in size, of former ferromagnesian minerals are entirely 

replaced by chlorite, epidote, calcite, and quartz. Magnetite grains 

are common and well dispersed throughout the groundmass__________ 1, 850 

Highly altered flow rock. Petrographic d·escription (sample 54 AKe 24) : 

Megas.eopieally a light-green-gray porphyritic rock. Microscopic examination indicates that the rock is an andesite vitrophyre that has been 

completely altered. The feldspar minerals are almost entirely destroyed ; the glass has devitrified to a chloritized cryptocrystalline aggregate (quartz?). Two remnant lithophysae are still discernible in 

the thin section. The mafic minerals have been completely replaced by 

chlorite (penninite?). Several laths of calcite were probably also derived from the altered mafic minerals. Pyrite is fairly common and 

minor limonite staining is presenL-------------------------------- 1, 830 

Porphyritic rock, greenish-gray, containing abundant phenocrysts 1 to 

2 mm in diameter. Petrographic description (sample 54 AKe 25): Microscopically the groundmass of the rock appears as a cryptocrystalline 

mass containing myriads of small uno:tiented microlites. The groundmass is clouded with magnetite dust, and chlorite is abundant. The 

phenocrysts consist of euhedral to subhedral laths of plagioclase feldspar and augite crystals. The predominance of labradorite suggests 

that the rock solidified as vitrophyric basalt, which has since. devitrified. The pyroxene crystals show varying stages of alteration ; some 

are partly altered to uralite, others are completely replaced by 

chlorite----------------------------------------------------------- :1,780 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 285 

Height 

above base of 

section 

(feet) 

Intensely altered 1low rock. Petrographic description (sample 54 AKe 

26) : A porous light-gray porphyritic rock containing many light-colored feldspar phenocrysts as much as 2 mm in size. The groundmass 

comprises a cryptocrystalline mass of quartz(?) and secondary quartz. 

The feldspar phenocrysts are partly altered to sericite, and those that 

are identifiable are in the labradorite part (Anto) of the plagioclase 

series. Abundant chlorite ( penninite?) and vein quartz fill many of 

the cavities and seams. Magnetite crystals are abundant. The rock 

may have solidified as andesite or, as is indicated by the plagioclase, 

vitrophyric basalt, but alteration makes positive identification impossible----------------------------------------------------------- 1,450 

Volcanic 1low rock. Petrographic description (sample 54 AKe 27) 

Dense medium-gray porphyritic rock containing many small (1 to 2 

mm) feldspar and pyribole phenocrysts. Microscopically the groundmass is seen to consist of a glassy base containing many needlelike 

microlites. Some of the microlites are arranged in subparallel 1low 

patterns about the phenocrysts. The plagioclase phenocrysts, predominantly in the labradorite range of the plagioclase series, are relatively fresh and unaltered. Many of the plagioclase crystals are zoned. 

Euhedral to subhedral phenocrysts of pyroxene are abundant. These 

crystals have undergone varying degrees of alteration, with uralite and 

chlorite replacing the pyroxene. Magnetite grains and limonite staining are present throughout the rock, which is vitrophyric basalt_ _____ 1, 350 

Altered 1low rock. Petrographic description (sample 54 Aka 28) : Megascopically a dense light-gray-green porphyritic rock containing abundant white phenocrysts (1 to 3 mm). Microscopically the groundmass consists largely of cryptocrystalline quartz. Many former feldspar crystals are indicated by lathlike crystal outlines now enclosing 

cryptocrystalline quartz and calcite. One incompletely altered andesine 

phenocryst was seen in the thin section. Small amounts of epidote 

and chlorite, probably derived from pyroxene, are present. Approximately 20 percent of the rock consists of chlorite ( penninite and ripidolite( ?) ) veins. A few pyrite cubes are also present_ ______________ 1, 250 

Altered extrusive rock. Petrographic description (sample 54 AKe 29) : 

Mottled gray-green rock containing many small (0.1 to 1 mm) white 

phenocrysts. The groundmass consists of secondary crystalline and 

cryptocrystalline quartz, chlorite, and shreds of sericite. The original phenocryst minerals have been entirely replaced, with only partial crystal outlines (as much as 0.5 mm in size) remaining. Uralite, 

chlorite, and epidote represent former ferromagnesian minerals, and 

patches of sericite and calcite may be alteration products of former 

feldsparminerals--------------------------------------------------- 350 

Altered extrusive rock. Petrographic description (sample 54 Ake 31) : 

Very similar to sample 54 AKe 29. Alteration is more complete, with 

the groundmass composed entirely of secondary quartz and chlorite. 

No distinct crystal outlines are present, but aggregates of sericite, 

quartz, chlorite, and calcite probably are alteration products of former 

feldspar and ferromagnesian minerals------------------------------ 300 
286 MINERAL RESOURCES OF ALASKA 

Height 

above base of 

section 

(feet) 

Altered extrusive rock. Petrographic description (sample 54 AKe 32) : 

Dense mottled light- to dark-gray rock. The groundmass is a chloritized aggregate of cryptocrystalline quartz, sericite, and calcite. There 

are no distinct phenocrysts, but aggregates of sericite indicate the former presence of feldspar minerals. Chlorite, with vague but discernible boundaries, indicates the former presence of some mafic minerals. 

Vein quartz and calcite are common, and limonite is disseminated 

throughout the rock------------------------------------------------ 220 

Altered volcanic flow rock. Dense medium- to light-gray aphanitic rock. 

Petrographic description (sample 54 AKe 21): The groundmass has 

the appearance of cryptocrystalline devitrified glass containing many 

microlites which compose about 20 percent of the groundmass. Fractured and altered phenocrysts of plagioclase are common and average 

0.4 to 0.6 mm in size. T'hose identified fall in the andestine-labradorite 

part of the plagioclase series. A few scattered phenocrysts of former 

ferromagnesian minerals are completely altered to chlorite. Magnetite 

dust and accessory pyrite are present------------------------------- 50 

Altered volcanic flow rock. Petrographic description (sample 54 AKe 

33) : A dense brownish-gray rock containing many small dark elongate 

phenocrysts as much as 3 mm in length. The rock has been completely 

altered. The groundmass is composed of a fine mosaic of cryptocrystalline quartz with interspersed calcite aggregates. Phenocrysts of schorlite indicate the former presence of feldspar minerals that have been 

altered by hot acid solutions. Small amounts of vein quartz and 

chlorite are present, and pyrite and limonite are accessory minerals___ 0 

The unit mapped as undeformed volcanic rocks (pl. 29) was not 

examined by the authors in the field. Differentiation of the unit is 

based in part upon examination of vertical photographs and in part 

upon the field notes of Werner Juhle and Ronald Kistler. The unit 

consists predominantly of flows of Quaternary age, but locally may 

include volcanic rocks of Tertiary age. 

TUFF 

Delineation of the tuff unit (pl. 29) is based on aerial reconnaissance of the area and examination of vertical aerial photographs. 

The emplacement of this thick tuff deposit prior to the 1912 eruption 

of Mount l{atmai has been discussed in great detail by Griggs ( 1922) 

and Fenner ( 1923) as volcanic sandflow. In addition, summary 

statements concerning this tuff deposit are presented by Curtis, 

Williams, and J uhle (in Luntey and others, 1954, p. 55-59). 

SURFICIAL DEPOSITS 

Surficial deposits in the l{atmai area are predominantly alluvial 

gravel and glacial moraine and gravel, but locally some ash and 

pumice deposits are exposed and a few small beach deposits may be 

seen along the shore. Individual lateral, terminal, and recessional 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 287 

moraines are shown on the geologic map (pl. 29}; other surficial 

deposits, including alluvial and glacial gravel, ash and pumice deposits, and beach deposits, are shown on the map as undifferentiated 

surficial deposits. 

INTRUSIVE ROCKS 

JURASSIC AGE 

Within the area mapped, intrusive rocks of Jurassic age crop out 

in a northeastward-trending belt 3 to 20 miles wide. The igneous 

body, which is of batholithic proportions, has been mapped in the 

Iliamna region to the north (Martin and Katz, 1912, pl. 2}, and as 

far south as Becharof Lake (Smith, 1925, pl. 4). In the Katmai 

area the intrusive body abuts the Naknek formation in fault relationship, and northwest of the fault it is overlain by layered volcanic 

rocks that are, in part, of Eocene age. The intrusive rocks cut the 

rocks older than Middle Jurassic in the vicinity of Kulik Lake. 

These intrusive rocks are variable in composition but consist predominantly of hornblende and biotite granite. Megoscopically the 

granite is light gray to pink. Along the southeast margin of the 

intrusive body the rock becomes darker and more mafic in 

composition. 

The exact age of the intrusive rocks cannot be postulated on the 

basis of their relationships with sedimentary units in the Katmai 

area. They are probably older than the Naknek formation, inasmuch as boulders of hornblende granite, probably derived from these 

rocks, occur as detritus within the Chisik conglomerate member of 

the Naknek formation. In the area adjoining the Katmai area on 

the north, Mather (1925, p. 166-167) notes that the intrusive rocks 

probably cut the Tuxedni formation of Middle Jurassic age. He 

further states (1925, p.167} that 

The granitic rocks in this and adjacent portions of the Alaska Peninsula are 

the results of several intrusions closely associated in time, but distributed 

at intervals throughout the Lower and Middle Jurassic epochs. 

J\Iather's work is the basis for the age which the authors have assigned to these rocks. 

TERTIARY AGE 

In many localities in the area, dikes and sills of Tertiary and 

Tertiary(~) age have intruded the beds of the Naknek and Kaguyak 

formations, which generally have low dips. Smith (1925, p. 198}, 

quoting notes of Fenner, reports "* * * many generally horizontal 

or gently inclined intrusions of hornblende andesite cutting the sedimentary rocks * * *" in the vicinity of Mount Katolinat. In addition, many dikes and sills, presumably of the same composition as 

those that intrude the sedimentary rocks at Katolinat, are present in 
288 MINERAL RESOURCES OF ALASKA 

the mountains at the headwaters of Gertrude and Takayoto Creeks 

and in the mountains northeast of Lake Grosvenor. In the latter 

area the upper several hundred feet of the mountain appears to be 

composed of sills. In addition, intrusive rocks of Tertiary age are 

known to be present in the vicinity of Geographic Harbor and Kukak 

Bay and along the fault south of Rallo Bay; and the crest of the 

Kamishak anticline is reported "* * * to be intruded by a quartzdiorite stock of post-Cretaceous age" (Hazzard, Bryan, and Borax, 

1950, p. 2377). 

Three samples of intrusive rocks of Tertiary age were collected by 

the authors; the descriptions follow: 

Quartz gabbro intruding the fault at Cape Nukshak (sample 54 AKe 37). 

Megascopically a light-colored phaneritic rock. Crystals of quartz, feldspar, 

and pyribole minerals are easily distinguished with a hand lens. Microscopically the rock is hypautomorphic and equigranular. The crystals average 

about 2 mm in size. Free quartz constitutes more than 5 percent of the rock. 

The feldspar is predominantly labradorite. A few of the feldspar crystals 

are partly epidotized. Pyroxene (augite) is altering to amphibole and chlorite. Accessory minerals include sphene, zircon, apatite, and magnetite. 

Quartz diorite collected on the southeast side of Kukak Bay (sample 54 AKe 

18). A light-gray-green phaneritic rock very similar in appearance to sample 54 AKe 37. Microscopically the rock is hypautomorphic and equigranular; it has undergone some alteration. The feldspar crystals average 2.5 mm 

in diameter. More than 3 percent quartz is present, some as micrographic 

intergrowths with potash feldspar. These intergrowths surround some of 

the abundant plagioclase laths that crystallized earlier. The plagioclase minerals are mostly oligoclase and andesine. The mafic minerals have been almost entirely replaced by chlorite, although a few amphibole relicts remain. 

Sericite replacement occurs along the feldspar fractures. A few crystals of 

sphene and much pyrite occur throughout the rock as secondary minerals, 

together with secondary calcite and chlorite. 

Quartz diorite collected on the southeast shore of Kukak Bay (sample 54 AKe 

20). A light-gray phaneritic rock spotted with dark-green pyribole minerals. 

Microscopically, a hypautomorphic granular rock with grains averaging 1.5 

mm in diameter. The feldspar grains are mostly alkalic. Crystals of hornblende are fairly common and are in various stages of alteration, from comparatively unaltered to completely chloritized. A few magnetite grains are 

present. 

STRUCTURE 

STRUCTURAL FEATURES 

The major structural feature in the area is a northeastward-trending fault that extends from the Kamishak River to Contact Creek, 

and is particularly well exposed about 2 miles northeast of Lake 

Grosvenor. This fault of presumed Tertiary age, upthrown on the 

north side, juxtaposes intrusive rocks of Early and (or) Middle 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 289 

Jurassic age with the sedimentary rocks of the Naknek formation. 

It is the southwestw~rd extension of the Bruin Bay thrust of the 

Kamishak .area (Hazzard, Bryan, and Borax, 1950, p. 2377), and it 

has been inferred ( Gryc, Miller, and Payne, 1951, fig. 5) to extend 

northward beyond Chinitna Bay and at least as far s<>uth as Becharof 

Lake (Smith, 1925, pl. 4). Within the mapped area, the fault generally has a steep dip. 

Northwest of the fault, volcanic rocks of Tertiary age dip gently 

:and monoclinally toward Bristol Bay. Southeast of the fault the 

regional southeasterly dip is interrupted by reversals, and, locally, 

gentle folds have developed within the sedimentary and volcanic sequences. Seven anticlines, all of which trend northeastward and in 

general plunge southwest or northeast toward the central part of the 

area, were mapped. No ma.rked asymmetry is evident in the anticlines, although the south flank of the Kamishak anticline is slightly 

steeper than the north flank. This anticline, the largest in the area, 

extends from the Savonoski River to the north margin of the map 

area and beyond, to Kamishak Bay, and plunges southwest where it 

:apparently dies out at the Savonoski River. 

Two small anticlines lie between Kejulik Pass and Kaguyak Crater. Most of the southwestern anticline is in volcanic rocks and lies 

along the trend of the chain of volcanoes between Martin Mountain 

and Mount l{atmai. It is delineated by dips in the flanking Naknek 

formation. The northeastern anticline, southwest of Kaguyak 

Crater, has the same general alinement. The two anticlines apparently do not connect, although they trend toward each other. Another 

anticline lies south of Topographers Peak, and three are formed in 

the volcanic rocks along the shoreline of Shelikof Strait. All four 

of these structures plunge northeast. 

The three synclines that have been mapped in the area have gentle 

flanks. The largest syncline extends from Gas Creek to Kukak Bay 

and is for the most part in volcanic rocks. 

In addition to the fault that transects the area from Little 

Kamishak River to Contact Creek, smaller faults are present. The 

largest of these is a westward-trending fault, which extends from 

Cape N ukshak to the volcanic spine of the Aleutian Range. Direction 

of throw on this fault is questionable. If, as it appears on vertical 

photographs, the volcanic beds on the north side of the fault are 

correlative with the volcanic rocks that overlie the Kenai formation 

on the south side, then the south side is upthrown relative to the 

north side. 

The volcanoes of the region, as already noted, are in northeasterly 

alinement. This alinement strongly suggests that the volcanic chain 
290 MINERAL RESOURCES OF ALASKA 

is structurally controlled. Surface outcrops, however, offer little 

evidence as to the nature of the control. The most reasonable assumption is that the two anticlines that are alined along the trend of the 

volcanoes are the manifestations of a deep-seated fault, and that the 

magma presumably followed zones of weakness not apparent in the 

surface outcrops of theN aknek formation. 

AGE OF THE FOLDING AND FAULTING 

It appears that there has been but one interval of major deformation 

since deposition of the Naknek formation, and the authors believe that 

this deformation probably occurred after Eocene and before Quaternary times. No angular unconformities are apparent between the 

formational units younger than Late Jurassic or older than Eocene. 

However, there is a definite angular break between the folded volcanic 

rocks that interfinger, at least in part,. with the Eocene rocks equivalent to the Kenai formation and younger undeformed volcanic rocks 

that are at least in part Quaternary in age. The authors therefore 

suggest that only one interval of deformation occurred, and that this 

was between the deposition of these two volcanic sequences. More 

precise dating of the folding and faulting is not possible with the 

present limited information. 

HISTORICAL GEOLOGY 

Inasmuch as no rocks older than Early Jurassic were studied in the 

field by the authors, only those events in geologic time since emplacement of the intrusive rocks of Jurassic age are considered in this 

discussion. These events have been reconstructed on the basis of the 

lithologic character of the rock units, their depositional relationships, 

their ages as established by the identification of the fossil lots by 

Imlay and Brown, and the structure in the map area. 

The emplacement of a batholith in Early and (or) Middle Jurassic 

time and subsequent uplift apparently created a positive land mass 

from which the arkosic conglomerate and feldspathic sandstone of 

the Naknek formation were derived. The Naknek formation changes 

very little anywhere along its strike in the area mapped, and its rocks 

seem typical of shelf deposits. The high percentage of feldspathic 

detritus within the formation suggests that the rock unit was deposited 

fairly close to its source, and the thick conglomerate beds and disseminated plant remains in the upper part of the formation are evidence of minor regressions of the sea in late Naknek time. 

A major hiatus, from Neocomian to Santonian time (fig. 45), sepa .. 

rates the Naknek and Kaguyak formations, and during the hiatus 

the Mount Katmai area was probably at base level. There is no 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 291 

apparent angular discordance between the Naknek and Kaguyak 

formations, and it is therefore unlikely that folding or faulting occurred between them. 

During Campanian time the seas transgressed the Mount Katmai 

area, and the marine lower member of the l{aguyak formation was 

deposited. The transgression was apparently followed by a gradual 

regression, and the more littoral middle and upper members of the 

Kaguyak formation were deposited. Locally, volcanic rocks, in part 

of Eocene age, directly overlie the Naknek formation, and it therefore 

appears either that part of the Mount Katmai area was completely 

emergent during the deposition of the Kaguyak formation or that the 

Upper Cretaceous rocks were eroded before the Eocene epoch. 

By Eocene time part of the Mount Katmai area was completely 

emergent. The coal-bearing rocks that are equivalent to the Kenai 

formation are typical of those deposited in lagoons, marshes, or along 

beaches, and the conglomerate lenses and beds may represent, in part, 

channel fillings along distributary strea.m courses. Early Eocene time 

was also one of volcanic activity, as indicated by the interbedded 

flows in the sedimentary sequence; it appears that environmental conditions during this period were not very different from those in the 

Mount Katmai area at the present time. The volcanic activity probably continued intermittently through Tertiary time, and the rocks 

of the map area were deformed between the Eocene epoch and the 

Quaternary period. Dikes, sills, and at least one stock were intruded 

into the sedimentary sequence during or following this deformation. 

Since the folding and faulting, the topography has been modified 

further by volcanic and fluviatile deposition and by glaciation and 

other types of erosion. 

PETROLEUM POSSIBILITIES 

The rocks of Mesozoic and Cenozoic age in the Mount Katmai area. 

lie in the arcuate belt of the Matanuska geosyncline (Payne, 1955). 

This geosynclinal belt extends northeastward almost to the Canadian 

border, and southwest of the Mount l{atmai area it parallels the south 

side of the Alaska Peninsula. Since the early 1900's a number of 

wells have been drilled in this geosyncline, mainly in the older Jurassic rocks. The closest of these wells to the map area is located about 

25 miles south of Katmai National Monument. Up to the time of 

writing of this report (1956), oil had not been found in commercial 

quantity, although oil shows had been found in most of the wells. 

Petroleum may be present in the map area, for oil and gas seeps 

have been reported. Martin {1905, p. 138) states that "Seepages have 

been reported from the shores of Kamishak Bay, especially at Douglas 
292 MINERAL RESOURCES OF ALASKA 

River," and Smith (1925, p. 206), states that "gas seepages on Gas 

Creek [at the headwaters of the Kejulik River] * * * occur for 

about 200 yards along the stream and issue from the loose boulders 

in its bed." To the knowledge of the authors, the Douglas River 

seeps have never been verified. 

STRATIGRAPIDC RELATIONS 

In the Mount Katmai area, 6,000 to 9,000 feet of Upper Jurassic 

marine fossiliferous rock, comprising arkose, siltstone, and shale, is 

exposed. The Upper Cretaceous rocks of the map area include 

4,500+ feet of marine shale, siltstone, and nearshore sandstone; abov:e 

this is 830 + feet of predominantly nonmarine sedi1nentary rocks of 

Eocene age. The rocks of Late Jurassic age could be both a source of, 

and reservoir for, petroleum, although in their belt of outcrop the 

sandstone units of the Naknek formation are tight and generally impermeable. The sandstone units in the middle and upper members 

of the Kaguyak formation cannot be dismissed as possible petroleum 

reservoirs. Furthermore the porous permeable sandstone of Eocene 

age may also, under special conditions, contain petroleum. 

Variables are such that it is not possible for the authors to predict 

the nature and thickness of the sedimentary rocks that might underlie 

the Naknek formation in the Mount Katmai area. These variables 

include unconformities as well as possible lateral variations in the 

rocks older than the Naknek formation. In addition, the southeast 

extent of the batholith emplaced in Early and (or) Middle Jurassic 

time can be determined only by geophysical work or by drilling. 

However, some idea of the sedimentary sequence older than the Naknek formation can be gained by a study of the literature dealing with 

localities north and south of the Mount Katmai area. 

About 30 miles south of the Mount Katmai area, at Puale Bay, 

rocks of Triassic as well as Early and Late Jurassic age are exposed 

below the Naknek formation. Kellum, Daviess, and Swinney (1944, 

fig. 2) mapped 2,250 feet of rocks of Late Triassic age at this locality; 

these rocks consist predominantly of thin-bedded limestone interbedded with sandstone and calcareous shale. Kellum, Daviess, and 

Swinney show a sequence of rocks of early Jurassic age that overlies 

the rocks of Triassic age and consists of about 1,050 feet of interbedded tuffaceous sandstone and limestone overlain by about 1,270 feet 

of rocks that are mostly shale. At Puale Bay, rocks of Middle 

Jurassic age are missing (Imlay, 1952, chart 8-C), and at least 5,000 

feet of conglomerate, sandstone, and shale (Smith, 1925, p. 196--,197) 

of the Shelikof formation of late Jurassic age overlies the rocks of 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 293 

Early Jurassic age and underlies the Naknek formation. Smith (p. 

196) states that "the formation apparently decreases in thickness toward the east from the head of Cold Bay [now Puale Bay], and some 

of the massive sandstone beds change laterally into shale." 

At U rsus Cove, about 30 miles north of the Mount Katmai are~ 

Martin and Katz (1912) mapped a sequence of Late Triassic age 

(the Kamishak formation) which is probably correlative with the 

Triassic sequence at Puale Bay, and they stated (p. 48) that it "probably exceeds 2,000 feet and may be much greater." They described 

the sequence as consisting of chert interstratified with thinner beds 

of limestone, shale, and sandstone. About 70 miles north of the 

Mount Ka.tmai area, west of the peninsula between Iniskin and Chinitna Bays, Hartsock (1954) mapped a thick sequence of volcanic 

breccia, lava, and andesitic tuff of Early Jurassic age, which overlies 

Triassic rocks. At this same locality the volcanic rocks are overlain 

by the Tuxedni formation of Middle Jurassic age; this includes 8,000 

feet or more of generally tight sandstone, siltstone, and shale (Kirschner, and Minard, 1949; Imlay, 1952; and Hartsock 1954). Overlying the Tuxedni and underlying the Naknek formation is the Chinitna formation, which Kirschner and Minard (1949) state "consists 

of approximately 2,000 feet of arenaceous siltstone" and which Imlay ( 1952) believes is correlative with the Shelikof formation at Puale 

Bay. 

The comparison of the rocks south and north of the Mount Katmai 

area is shown on figure 46. The occurrence of petroleum in these 

older rock units appears to be most likely in the rocks of Late Triassic age; these may lie as deep as 15,000 feet below the base of the 

Naknek formation in the Mount Katmai area, if judged by the thicknesses of the older rock units to the south and to the north. 

STRUCTURAL RELATIONS 

The authors do not rule out the possibility of producing oil from 

structural and stratigraphic traps in the Mount Katmai area, but 

believe that in general the area is not very promising. The area 

has been subjected to intense igneous activity, and it is unlikely that 

favorable petroleum strata can be reached at practical drilling depths 

on most of the structures that could be drilled. 

Seven anticlines and one major reverse fault are present in the 

map area. The largest anticline is the Kamishak, which the authors 

believe to be a closed structure on the basis of Mather's map (1925, 

pl. 3) and their fieldwork. However, there are two drawbacks to 

drilling this anticline. It has been intruded at the crest by a quartz 

diorite stock (Hazzard, Bryan, and Borax, 1950), and the depth to 
294 MINERAL RESOURCES OF ALASKA 

s Puale Bay .. U rsus Cove and Iniskin rll (I) Peninsula .jJ .9:1 After Imlay (i952), Kellum, Daviess, and -rll ,.. Swinney (1944), and Smith (1952) After Hartsock (1954), Imlay (1952), >. (I) 

00. 00 Kirscher and Minard (1949), 

and Martin and Katz (1912) 

Naknek formation Naknek formation ,.. 

(I) 

Shelikof formation 8: Chinitna formation 

::> 5000feet 2000 feet Conglomerate, sandstone Arenaceous siltstone and shale 

·~ .$ Tuxedni formation 

::::s re Not represented 8000+ feet ~ re 

-:i Impermeable sandstone, si:tstone, 

and shale 

? ? ? 

,.. Unnamed formation Unnamed formation · (I) 

~ 1270 feet shale Thickness unknovm 0 

~ 1050 feet tuffaceous sandstone and Volcanic breccia, lava, and andesitic 

limestone tuff 

.S:l ,.., Unnamed formation Kamishak formation 

~ 8. 2250+ feet 2000+ feet s:l. ·;::: ::> Thin-bedded limestone, sandstone, and Chert, limestone, shale, and sand- E-4 calcareons shale stone 

FIGURE 46.-comparison of Naknek and older formations south and north of the Mount 

Katmai area. 

a potentially favorable stratum may be beyond the limits of a practical drilling test. 

The two anticlines that transect the central part of the map area. 

are closely related to the alinement of the volcanic chain, and· are 

probably a reflection of the deep-seated structural control of this 

alinement. If they are, the chances of producing oil from either of 

the two are not good. 

The anticline south of Topographers Peak, the one that cuts Dakavak Lake, and the one between Katmai Bay and Geographic Harbor, all plunge northeast. The authors have not studied these anticlines in detail, but it is their opinion that none are closed structures. 

The authors are not prepared to say whether the anticline that 

lies between Kinak Bay and Kaflia Bay is a closed structure. It 

is formed in dense volcanic rocks that may overlie rocks of Cretaceous age as well as Jurassic age, and although the thickness of 

the volcanic sequence is not known, the older rocks, which cannot be 

ruled out as possible oil reservoirs, may be within drilling depth. 

However, the fieldwork of the authors was not detailed enough to 
GEOLOGY OF THE MOUNT KATMAI AREA, ALASKA 295 

rule out the possibility that the anticline has been intruded by igneous 

rock. 

The reverse fault that extends from the Little Kamishak River to 

Contact Creek is the largest structural feature in the area. No potential drilling sites are readily apparent along this fault, although 

the strikes of the Naknek formation south of Y ori Pass, south of 

Angle Creek, and west of Kejulik Pass, indicate that there may be 

-closure against the southeast side of the fault along Contact Creek. 

The intrusive body that lies along the northwest side of the fault is 

presumed to be of Lower and (or) Middle Jurassic age, and if it is, 

it may underlie the Naknek formation on the southeast side of the 

fault. If it does, the chances of striking a petroleum bearing zone 

in a drill test near Contact Creek are not good. 

As already noted, Smith ( 1925, p. 206) reported gas seeps "along 

a fault at 'Gas creek." The seeps were not visited by the authors, 

and their source and nature are not known. Possible drilling sites 

could not be delineated from vertical photographs of this vicinity. 

SELECTED REFERENCES 

Atwood, W. W., 1911, Geology and mineral resources of parts of the Alaska 

Peninsula: U.S. Geol. Survey Bull. 467, 137 p.,14 pls. 

Dan, W. H., 1898, A table of North American Tertiary horizons, correlated 

with one another and with those of western Europe, with annotations: U.S. 

Geol. Survey 18th Ann. Rept. pt. 2, p. 323-348 . 

. Dall, W. H. and Harris, G. D., 1892, Correlation papers, Neocene: U.S. Geol. 

Survey Bull. 84. 

Emerson, B. K. and others, 1904, Alaska, v. 4, Geology and paleontology [Harriman Alaska Expedition]: New York, Doubleday, Page and Co. 

Fenner, C. N., 1920, Geology of the Katmai region, Alaska, and the great eru~r 

tion of 1912 [abs.]: Geol. Soc. America Bull., v. 31, no. 1, p. 140. 

-- 1920, The Katmai region, Alaska, and the great eruption of 1912: J'our. 

Geology, v. 28, no. 7, p. 569--606, 17 figs. 

-- 1922, Evidences of assimilation during the Katmai eruption of 1912 

[abs.]: Geol. Soc. America Bull., v. 33, no.1, p. 129 . 

.....__ 1923, The origin and mode of emplacement of the great tuff deposit in 

the Valley of Ten Thousand Smokes: Natl. Geog. Soc., Contributed technical papers, Katmai series, no. 1, 74 p. illus.; also, [abs.], Science, new 

ser., v. 57, p. 446-447 . 

.....__ 1925, Earth movements accompanying the Katmai eruption: Jour. Geology, v. 33, no. 2, p. 116-139; no. 3, p. 193-233, 18 figs. 

Griggs, R. F., 1922, The Valley of Ten Thousand Smokes: Washington, Natl. 

Geog. Soc., 340 p., 16 pls., 217 figs., 9 maps. 

Gryc, George, Miller, D. J., and Payne, T. G., 1951, Alaska, in Ball, M. W., ed., 

Possible future petroleum provinces of North America : Am. Assoc. Petroleum Geologists Bull., v. 35, no. 2, p.151-168. 

Hartsock, J. K., 1954, Geology of the Iniskin Peninsula and adjacent areas, 

Alaska: U.S. Geol. Survey open-file report. 
296 ~ERAL RESOURCES OF ALASKA 

Hazzard, J. C., 1950, Lower Cretaceous rocks at Cape Kaguyak north of Kukak 

Bay, Alaska; Science, v. 112, p. 227. 

Hazzard, J. C., Bryan, J. J., and Borax, Eugene, 1950, Geology of Kamishak 

Bay area, Cook Inlet, Alaska: Am. Assoc. Petroleum Geologists Bull., v. 34, 

p. 2377. 

Hazzard, J. C., Bryan, J. J., Borax, Eugene, and Shoemaker, R., 1950, Cretaceous rocks in the Kamishak Bay area, Cook Inlet, Alaska: Science, v. 

112, p. 226-227. 

Imlay, R. W., 1952, Correlation of the Jurassic formations of North America, 

exclusive of Canada: Geol. Soc. America Bull., v. 63, p. 953-992. 

Imlay, R. W., and Reeside, J. B., 1954, Correlation of the Cretaceous formations of Greenland and Alaska : Geol. Soc. America Bull., v. 65, no. 3, 

p. 223-246. . 

Kellum, L. B., Daviess, S. N., and Swinney, C. M., 1944, Columnar sections and 

correlation chart of rocks at Wide Bay and Cold Bay, Alaska: U.S. Geol. 

Survey war minerals investigations. 

Kirschner, C. E., and Minard, D. L., 1949, Geology of the Iniskin Peninsula, 

Alaska: U.S. Geol. Survey Oil and Gas Inv. Map 95. 

Knappen, R. S., 1926, Geology and mineral resources of the Aniakchak district: 

U.S. Geol. Survey Bull. 797, p. 161-223. 

Luntey, R. S. and others, 1954, Katmai National Monument: U.S. Natl. Park 

Service Interim Rept. 

Martin, G. C., 1905, Notes on the petroleum fields of Alaska, in Brooks, A. H. 

and others, Report on progress of investigations of mineral resources in 

Alaska in 1904: U.S. Geol. Survey Bull. 259. 

--- 1926, Mesozoic stratigraphy of Alaska; U.S. Geol. Survey Bull. 776. 

Martin, G. 0., and Katz, F. J., 1912, A geologic reconnaissance of the Iliamna 

region, Alaska: U.S. Geol. Survey Bull. 485, p.1-138. 

Mather, K. F., 1925, Mineral resources of the Kamishak Bay region, in Brooks, 

A. H. and others, Mineral resources of Alaska: U.S. Geol. Survey Bull. 773, 

p.159-181. 

Muller, E. H., 1952, Glacial history of the Naknek district, Alaska Peninsula, 

Alaska : Geol. Soc. America Bull., v. 63, p. 1284 . 

.____ 1953, Northern Alaska Peninsula and Kilbuck Mountains, Alaska, in 

Pewe, T. L. and others, 1953, Multiple glaciation in Alaska, a progress 

report: U.S. Geol. Survey Circ. 289, p. 2-3. 

Muller, E. H., Juhle, R. W., and Coulter, H. W., 1954, Current volcanic activity 

in Katmai National Monument, in Luntey, R. S., and others, Katmai National Monument: U.S. Natl. Park Service Interim Rept. 

Payne, T. G., 1955, Mesozoic and Cenozoic tectonic elements of Alaska: U.S. 

Geol. Survey Misc. Geol. Inv. Map I-84. 

Pewe, T. L., and others, 1953, Multiple glaciation in Alaska, a progress report, 

U.S. Geol. Survey Circ. 289. 

Smith, P. S., 1939, Areal geology of Alaska: U.S. Geol. Survey Prof. Paper 192, 

p. 62-63. 

Smith, W. R., 1925, The Cold Bay-Katmai district, in Brooks, A. H. and others, 

Mineral resources of Alaska: U.S. Geol. Survey Bull. 773, p. 183-207. 

Spurr, J. E., 1900, A reconnaissance in southwestern Alaska in 1898: U.S. 

Geol. Survey, 20th Ann. Rept., pt. 7, p. 43-263. 
IN;DEX 

Acknowledgments •• -------------------------- Alnm .. __ .. ___ ------ ________________________ _ 

alas kana ____________________ ------- ______ _ 

Amoebocera.t (Prionodoceraa) ------------------

Page 

264 

282 

282 

273 

zone ___ ----------------------------------- 273 

Ammonites ____ ------_--- __ -----------------__ '1:77 

Amphibole.-------------------------------- 276,288 Andesine _______________________ 276,280,284,285,288 

Anomia vancouveren.ti•------------------------ 277 

Anticlines ______________ 269,280,288,289,290,293,294 

Apatite ______________ ----- _________ -____ -----_ 288 

ABtarte sp ____ -------------------------------- '1:72 

Aucella bronnL------------------------------ 273 

concentrica ____ ___ ------- ______ • ___ ------- _ 273 

moBquenais------------------------------ 272,273 TUU(l8a _______________ ._ __________________ 272, '1:73 

SP---------------------------------- 270,271,272 Augite ______________________________ '1:76, 280,284,288 

Batholith, emplacement ____________________ 290,292 

BelemniteJJ sp ___________ ---------------------- 272 

Betu.la ___ -- ______ ----------------------------- 282 

Biotite._----------------------------------- 270, 287 

Bone fragment •• ----------------------------- 272 

Brachiopods·----------------- _______ -------__ 272 

Calcite.-------------------- 280,281,284,285,286, 288 

Cardiocera.t sp_. __ ---------------------------- 273 zone .. --------- ____ --- _____________ ----___ 273 

Cercidiph11llum ellipticum_____________________ 283 

Chinitna formation--------------------------- 293 

Chlorite ____________________ 280,281,284,285,286,288 

Coal-bearing rocks, age and correlation._._ 281-282 

defined _________ -------- _____________ ----- 278 

fossils.---------------------------------- 281, 282 occurrence and lithology__________________ 278 

stratigraphic sections ___________________ 278-281 

Cosstlines, ~haracteristics. ------------------- 267 

CoT'I/lm ___ ______________ --------- _______ ------ 282 

Page 

Gas seeps __________________________________ 291,295 

Gaudruceraa denmaneme •• -------------------- 277 

Geography __ --------------------------------- 262 

Geologic formation.<~, generalized section._--__ 274 

Glaciation __________________ 265,266-267, 28&-287, 291 

GluptoBtrobm dakotemis.---------------------- 282 

Historical geology_------------------------- 29o-291 

Hornblende __ ------------------------------ 287,288 

Hazzard, J. C., quoted_______________________ 275 

Imlay, R. W., quoted __________________ 272-'1:73, 277 

Imlay, R. W., and Reeside, J. B., quoted .. 277-278 

Inoceramus kuairoensia .• ---------------------- 277 

.thikotanen.ti.t ... _ -------------------------. 277 

aubundatua •. _ ---------------------------- 278 

sp. ____ -------- __ . ___ - __ • ----------------- 277 

Introduction. __ ------------------------------ 262 

Intrusive rocks, description___________________ 288 

lithologic character_---------------------- 287 

Tertiary age___________________________ 287-288 

Investigation, methods.---------------------- 263 

previous •..•• --------------------------- 263-264 

Kaguyak formation, age and correlation ••.• 277-278 

defined_. _____ -------_------------_----- 273-275 

deposition .• ------------------------------ 291 

d1kes and sills____________________________ 287 

fossils •• ---------------------------- 275, 277-278 

hiatus. ____ ---- ___ ---------------------- 29Q-291 

occurrence and lithology__________________ 275 

petroleum possibilities-------------------- 292 

stratigraphic section ____________________ 275-277 

Kamishak anticline ________________ 269, 288, 289, 293 

Kamishak River, course---------------------- 266 

Katmai River, course---------------------~- 265,266 

Kenai formation ___________________ 281-282, 283, 290 

Dall, W. H., and Harris, G. D., quoted------

Dicotyledonous leaves •. ---------------- 275,282,283 

Dikes._-------------------------------- 287-288, 291 

Diplomocera.t notabile_________________________ 277 

Drainage, lakes_______________________________ 266 

278 Labradorite ••• -------------------- 280, 284, 285, 288 

Lima sp. _ ------------------------------------ 272 

rivers _________________________ ----- _____ 265-266 

Epidote._---------------------------------- 284, 285 

Eumicrotia SP--------------------------------- 272 

Faults __________________________ 288,289,290,293,295 

Feldspar_---------- 271,276,280,281,284,285,286,288 

Folding and faulting, age.-------------------~ 290 

Limonite-------------------------- 280,284, 28b, 286 

Lvtoceraa (GaudT'I/cera.t) SP-------------------- 277 

Magnetite------------------------- 284, 28b, 286, 288 

Magnolia SP---------------------------------- 282 

Martin, G. C., quoted _____________ 274-275, 291-292 

Matanuska formation.----------------------- 277 

Matanuska geosyncline_______________________ 291 

Mather, K. F., quoted----------------------- 287 

M.eleaorineUa SP------------------------------ 272 

Metasequoia occidentali.t--------------------- 282, 283 

297 
298 INDEX 

Page 

Naknek formation, age and correlation _____ 271-273 

Chisik con~lomerate member __ 269, 270, 273, 287 

comparison .. ______________ ---____________ 294 

defined ______ ----------------------------- 269 

dikes and sills __ -------------------------- 287 

fault_ __ -------------------------------- 289, 290 

fossils __ ------------_--------------- 270, 271:...273 

hiatus ______________ -------------------- 29G-291 

occurrence and llthology ---------------- 269-270 

petroleum possibilities____________________ 292 

stratigraphic section______________________ 271 

Nemodon SP---------------------------------- 277 

Oligoclase ___ ------------------------------- 284, 288 

Pachydiscul! ootacodensif!_______________________ 277 

suciaensis ___ _ -- __ ------ __ ------- _ -- _ ------ 277 

PageSpurr, J. E., quoted------------------------ 268, 26~ 

Stock ___ ------------------------------------ 291,293: Stratigraphic relations ______________________ 292-293' 

Structural features·------------------------- 288-290. 

Structural relations ... ---------------------- 293-295 

Surficial deposits. See Unconsolidated deposits. 

Synclines __________________ ------------------- 289> 

Talc __________________ ---------------------___ 284 

Topography-------------------------------- 264-265· Tuff, andesitic________________________________ 293: 

deposit _____ ----------------------_------- 286 

Tu.rbo sp ___ ---------------------------------- 272' Tuxedni formation ___________________ .; _____ 287,293 

(Neodesmoceras) sp_- --------------------- 277 Ukak River, course.-------------------------- 265. 

Pectinoid pelecypods_------------------------ 2il Unconformities ________________ ------------- 290, 292' 

Penninite_-- ------------------------------- 284, 285 Unconsolidated deposits ____________________ 286-287 

Petroleum possibilities _____________ 291-292,293,294 Uralite.------------------------------------ 284,285-

Phylloceras ramosum__________________________ 277 

sp_ --------------------------------------- 272 Volcanic rocks, description ___ -------------- 284-286. 

Plagioclase __ --------------- 276, 280, 281, 284, 285, 286 layered.---------------------------------- 287 

Pleuromu- SP------------------------------- 272,277 sequence_-------------------------- 282-283,290. 

Pumice, deposits ... ------------------------ 286,287 total thickness .... ------------------------ 283 

Pyribole minerals_--------------------------- 288 unconformity----------------------------- 290. 

Pyroxene ___ ---------------------------- 284, 285, 288 undeformed.----------------------------- 29() 

Pyrite·------------------------- 276,284,285,286,288 Volcanic sandflow -----· ---------------------- 286 

Volcanism, history------------------------- 282,291 

Quartz ___ ---------- 271, 278, 279, 281, 284, 285, 286, 288 recent_·------------------------------____ 268 

Volcanoes, alinement_ __________________ 289-290,294 

Knife Peak Volcano •• ------------------ 264,268 Kukak Volcano ________________________ 264, 26S 

Martin Mountain •• -------------------- 264; 268 

Reeside, J. B. See Imlay, R. W. 

Rhynchonella sp ___ ---------------------------

Ripidolite ______ ------------------------------· 

272 

285 

Savonoski River, course______________________ 265 Mount Denison •• ------------------------ 264 

Schorlite .•••• -------------------------------- 286 Mount Douglas •• ---------------------- 264,268 

Sericite.-------------------------------- 285,286,288 Mount KatmaL-------------- 264,267, 2f.S, 286 

Shelikof formation____________________________ 292 Mount Mageik _________________________ 264, 26S 

Sills. __ ----------------------------·---- 287-288, 291 Novarupta Volcano .• -------------------- 268 Smith, P. S., quoted_________________________ 2!U Snowy Mountain_________________________ 264 

Smith, W. R., quoted ______________________ 287,293 Trident VolcanO---------~-------------- 264, 26S 

Sphene __________ ------- __ -------------------· 288 Zircon .• ----------------------------------·--- 288 

0