UNITED STATES DEPARTMENT OF THE INTERIOR

BULLETIN 1028 PLATE 41

53°
27
30"

53°

GEOLOGICAL SURVEY
168° 15' 168° 00"
Cape Tanak
om Ashishik
&
&
&
“yy
CG
SEA
Cape
Chagak Cape Idak

Cape Aslik

Cape
Kigunak

Satellite Field

TRUE NORTH

Aguliuk Point ; ~ Z
C Vi ’ p ZY oy . : Wi iy
\\ \ 3 Z : y Yyds y, he Gy,

b é yl LED \ WYLIE
y Ky a : : zs eS ; es ifs Z Lo EXPLANATION

ign.
fees Ls <2
WY yeep Ua i SURI
Zu jo, Z FICIAL DEPOSITS =
Uy % s @
,, ty § [eo | | at ] | Qal [ Qbs ] [- z
ty ir
WME GLA GI Ti Talus and Alluvium Beach deposits Dun E
other eolluvium <
IGNEOUS AND METAMORPHIC ROCKS S
aat 5
Qat
LH,
£ Bs,
a
4
&
co >
€
=
& Basaltic flows later than Caldera Lake
2 Qafs, Basalt flows from cone A in 1945;
§ Qat, Pre-1945 basalt flows from cone A
? Obi, Basaltic andesite 7m cone
2 £ B; Qut, Wall-fiseure flows; Qet, Basalt
z 3 8 from cone E; Qi, Basalt flows
3 8g ‘from cone F
3 =
z rl Ss
Basalt flows outside Vent lava, g ee es
‘Okmok Caldera undifferentiated & . =I
Qc, Cinder cone =<
deposits 3
a Rocks contemporaneous with Caldera Lake
Qs, Bedded volcanic sediments; Qod, Plagioclase
basalt flows from cone C and D; Qep, Early
post-cdldera pyroclastic rocks
e
H
5
| Okmok voleanies
<p $ Pyroclastie rocks deposited by ealdera-formi:
5 wreand Guriat wlcana' Necoheon her
5 Yeas than 10 ft thick. Also includes possibly
4 ee clecde Paceaten marth cn one
| & arcuate ridges
1
i Le]
k P . Crater Creek basalt
2 23
S g2| EE [Le | fe] S|
ss] 28 -—
$e. EZ | Vitreous andesite Rhyolite Plagioclase-olivine basalt of satellitic vents
& 2) By Qbo, Plagioclase-olivine basalt flows
Ship Rock = ; i a by, Vent complex or voleanic neck
\ gc) ef |
g lle Pe
Fy Mafic phenoeryst _Palagonitized Aphyric and feldspathic basalt |
2 IP
\ < basalt, pyroclastic rocks QTab, Aphyric and feldspathic basalt flows |
| QTai, Aphyric and jeldspathic basalt intrusives |
ints ! UNcoNFoRMITY |
| |
| Qld) I
| bs rE
| =
Voleanie rocks of central Umnak fe
! QTy, Hydrothermally altered voleanic rocks | Ui
| typ, Vent and intrusive compler; includes | =
a few unaltered rocks: QTvg, Intensely al-
| tered, silicified, potassium feldspathized
reel
Contact
Dashed where approzimately located
Indefinite contact
Gradational and inferred
Se ercess
D
High-angle fault
Dashed where approzimately located,
dotted where, concealed; Us, upthrown
side; D, downthrown aide
> Coneesled or hypothetical fault
% a2
G Strike and dip of layered rocks
168° 00” 0 c)
Horizontal layered rocks
Cinder
Point =.
Direction of glacial striae
LJ
ca
Steeple 5 1 G
Point Kettle Cape 1 ¥
A
oKMOK CALDERA ,
Jag Peak Ss 4000"
Cone E B 3000

Ashishik basalt

{| BeRING SEA

Ashishik basalt Breccieted rocks of precaldera age

Mount Tulik

North Arcuate
B Ridge oK MO K fg CALDERA Qo B
4000+ a fe 4000"
5 : ab
30004 5 S & fs000"
g g & a
2000 2 beo00!
ak QTab & 3 S
100044 §§ — = S  frooo!
& aR peer cee Qs =
Sua fore! Lees Ashishik basalt SEER css saves
1000' + 1000°
2000'. 2000

Base compiled from U. S. Army Engineers quadrangles INTERIOR GEOLOGICAL SURVEY, WASHINGTON, B.C
1-8, 11-13, Grid zone “D” Band Il N

GEOLOGIC MAP AND SECTIONS OF NORTHEASTERN UMNAK ISLAND, ALEUTIAN ISLANDS, ALASKA

Scale 1:63 360

1 0 1 2 3 4 5 Miles

Contour interval 200 feet
Datum is mean sea level

Geology by F.M. Byers, Jr., David M. Hopkins
and Bernard Fisher, 1946 and 1947