UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

179°10°

179°15/

179°20'

179°25'

BULLETIN 1028 PLATE 69
179°30'

© ° 0 05!
178°30' 178°35! 178°40' 178°45) 178° 50! 178°55! 179°00" 179°05' a
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51°40"
51°40’
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air 178° 50! 178°55) 179° 00 179°05! 179° 10" 179°15/ 179°20' 179°2! 179° 30°
Geology by H. A. Powers, R. R. Coats, and others,

178° 30" 178°35!
Island topography reduced from U. S. Coast and Geo-
detic Survey manuscript sheets T5593-T5600, scale
1:20 000. Submarine contours by H. A. Powers from
U. S. Coast and Geodetic Survey smooth sheets from
hydrographic surveys, 1934-52

178°40°

178° 45/

TOPOGRAPHY OF PART OF THE ALEUTIAN RIDGE AND GEOLOGIC MAP OF AMCHITKA ISLAND, ALASKA

1 2 3

5 Miles

Contour interval 100 feet
Datum is mean sea level
Depth contours in feet
Contour interval 100, 200, 300, and 600 feet
Supplemental contour interval 25 feet

1946-51

Recent

Pleistocene

Oligocene or Miocene

EXPLANATION

Alluvial and eolian deposits
Unconsolidated material in valley floors, Qal; a few
cliff-top dunes, Qd

Glacial and interglacial deposits

Till, outwash gravel, and silt with varvelike bedding,

Qg, that contain constituents not of local origin.

Beach deposit of sand, cobbles, boulders, and shells

of marine fauna characteristic of warmer water, Qb.
Inferred late interglacial age

ws |
Tilted sedimentary rocks at South Bight

Sund and silt in tilted beds, truncated at 90-foot alti-
tude, overlain by fossiliferous beach deposit

Gravel of hornblende andesite
Sand and gravel, nonindurated, bedded, composed of
fragments of porphyritic hornblende andesite. Infer-
red beach and nearshore marine deposit

SQTe

Chitka Point formation

Flows, flow breccias, and dikes of porphyritic andesite

and feldspathic basalt, in part interbedded with

marine conglomerate, in part subaerial deposits.
Thickness exceeds 1000 feet

Quartz diorite

Medium-grained quartz diorite and related rock in

dikes, sills, and a small stock. Intrudes rock of
Amchitka and Banjo Point formations

=]
Banjo Point formation
Sandstone, conglomerate, tuffaceous shale, and lapilli
tuff of basaltic composition. Bedded, near-shore

marine deposits containing sparse fauna of middle
Tertiary age

Amchitka formation

Volcanic agglomerate, tuff-breccia, tuff, and pillow

lava flows of andesitic to latitic composition. Tilted,

jointed, and slightly metamorphosed in many areas.
Thickness several thousand feet

1?
Contact, showing dip
Dashed where location is inferred

*
D
ot —-----
Fault, showing dip
Dashed where inferred from physiographic lineations
on aerial photos. U, upthrown side; D, downthrown
side

ae

Approximate strike and dip of beds

Base of abandoned sea cliff,
showing altitude or depth

———— 0 —
Shelf-break, showing depth

Deb

TAN
Knobs and depressions on submerged bench, showing
top of the knobs and bottom of the depressions

ross

A A
Profile in figure 78

a
Bs

TRUE NORTH
MAGNETIC NorTA

APPROXIMATE MEAN
DECLINATION, 1959

QUATERNARY

TERTIARY OR QUATERNARY

TERTIARY

TERTIARY OR OLDER