ment. Thickness as much as several
River. Several meters exposed at a few
meters. Contacts well defined, but width
places along the Eagle River, but only 1 m
shown on map may be exaggerated to
or a few meters in roadcuts. Kenai Group
accommodate linear base-map symbols
present at depth beneath surficial deposits
provided for roads and railroads. Mapped
throughout most of the Anchorage Low-
mainly along Glenn Highway and the
land, where thickness of surficial deposits
Alaska Railroad, at some airfield runways,
may be as much as 100 m. About 15 km
and along some streets within the urban-
southwest of the Eagle River, however,
ized area, especially where they cross low-
Sterling Formation (overlying the Tyonek)
lying places. Minor fill for roads not shown.
has been tentatively identified (Stricker et
al. 1988) in a drill hole (Yehle et al. 1986),
and this formation probably constitutes
Bedrock
Bedrock is not shown in detail here. It is subdi-
part of the total thickness of Kenai Group
vided into two units, younger bedrock and older
rocks southwest of the Eagle River.
bedrock. Younger bedrock comprises sedimen-
bo
Older bedrock (Tertiary to Permian)--
tary rocks of Tertiary age and is confined to a few
Predominantly rocks of the Chugach ter-
outcrops in the margins of the Anchorage Low-
rane: McHugh Complex occupies most of
land. Older bedrock includes rocks of both
the mountainous area; Valdez Group
Chugach and Peninsula tectonostratigraphic ter-
occurs near South Fork Eagle River and
ranes (Coney and Jones 1985, Jones et al. 1987,
on part of the ridge between it and Ship
Silberling et al. 1994) and consists of variably
Creek Valley. Rocks of the Peninsula ter-
metamorphosed sedimentary and igneous rocks.
rane crop out in the margins of the
It is exposed only in the Chugach Mountains and
Anchorage Lowland and may occur on
in narrow canyons where major streams are
ridges near Parks and Little Peters Creeks
incised in the Hillside area and just northwest of
as well. The two terranes are separated by
the mountain Front. Where mapped on mountain
the Border Ranges fault (MacKevett and
slopes, bedrock may be concealed by thin col-
Plafker 1974) which, however, is mainly
luvium.
or perhaps entirely concealed beneath
surficial deposits within the map area.
by
Younger bedrock (Tertiary)--Continental
McHugh Complex (Clark 1973) consists
rocks, mainly sandstone, siltstone, clay-
principally of a metaclastic sequence in-
stone, and minor coal of the Kenai Group
cluding variably metamorphosed gray-
(Calderwood and Fackler 1972). Tyonek
wacke, argillite, phyllite, and conglomer-
Formation (Wolfe and Tanai 1980) is
atic graywacke; locally consists of a meta-
exposed locally along lower course of the
volcanic sequence including greenstone,
Eagle River where two fossil-plant locali-
metachert, cherty argillite, and argillite.
ties have been examined by Schaff (1964)
Valdez Group includes principally meta-
and by Wolfe et al. (1966). It is likely that
graywacke, metasiltstone, and argillite;
this is the formation present at scattered
felsic to intermediate hypabyssal intru-
roadcut localities within about 2 km of the
sive rocks are present in and west of the
Chugach Mountain Front in the vicinity of
canyon near the mouth of the South Fork
the community of Eagle River, and north-
Eagle River. Peninsula terrane rocks con-
ward along the Glenn Highway (Dobrov-
sist mainly of metasedimentary and meta-
olny and Miller 1950, Schmoll et al. 1971,
volcanic rocks including metasandstone,
Zenone et al. 1974). Similar rocks may
metachert, siliceous argillite, marble, and
occur in poor exposures along the Glenn
greenstone (descriptions and distribution
Highway about 3 km south of the Eagle
from Clark 1972 and Winkler 1992).
68
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