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Colluvial deposits on mountain slopes
Mixed colluvial and glacial deposits (Holo-
(Holocene and Pleistocene)--Mainly apron-
cene and Pleistocene)--Diamicton; may
like deposits of loose, sandy to rubbly
include chiefly gravelly to rubbly sand,
diamicton derived directly from weather-
with some silt and clay; locally bouldery.
ing of bedrock upslope; include some sheet-
Derived from both bedrock and glacial
wash deposits. Thickness probably less
deposits, either of which may be present in
than 1 m to several meters, thicker on lower
areas too small to map separately. Poorly
parts of slopes. Contacts gradational. Top-
bedded and sorted. Loosely to moderately
ography smooth, surface gently concave,
compacted in most places. Thickness a few
slopes generally steep to very steep, but
to several meters. Contacts gradational.
usually not in excess of 70%. Commonly
Slopes smooth to slightly irregular, steep
veneered by thin, low vegetation. Some
to very steep. Common along middle
instability likely. Occur on mountain slopes
slopes of most major mountain valleys
in a belt downslope from mapped bedrock.
and along Chugach Mountain Front where
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Talus deposits (Holocene)--Cone-shaped to
glaciers formerly abutted the slope but
apronlike deposits on valley walls within
few identifiable glacial deposits are
rugged mountains. Mainly loose, coarse
present at the surface.
cm
rubble, and rubbly diamicton derived
Colluvial deposits derived mainly from
directly from weathering of bedrock up-
moraines (Holocene and Pleistocene)--
Diamicton similar to that of adjacent up-
slope. Thickness variable, generally thick-
slope moraines, but less compact. Include
est in middle to lower parts of cones and
minor amounts of better-sorted sand, silt,
aprons, probably several to a few tens of
and gravel that occur in irregular beds and
meters, thinning gradually upward towards
that may have been derived from better-
apexes and more abruptly downward near
sorted glacial deposits and moved partly
toes. Contacts generally gradational, to bed-
with the aid of running water. Commonly
rock at apex and to other mapped units at
a few meters thick. Contacts generally gra-
toe; individual cones commonly have well-
dational, especially upslope. Slopes gener-
ally moderate and moderately stable.
its too small to map separately are included
Commonly associated with lateral mor-
in bedrock map unit. Topography smooth,
aines along the Chugach Mountain Front
slopes steep to very steep, as much as 100%
and in a few places in mountain valleys.
near apex, rarely less than 35% near toe.
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Commonly free of even low vegetation and
Colluvial deposits on walls of inlet and
subject to continuing deposition from ups-
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stream bluffs (Holocene and late Pleis-
lope, including rockfalls and debris-laden
tocene)--Loose accumulations that are
snow avalanches; slopes generally unsta-
derived from adjacent, upslope surficial
ble. Occur locally on highest and in associa-
deposits and that form a veneer on bluffs
tion with steepest mountain slopes.
after active erosion has ceased. Chiefly
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diamicton, consisting of pebbly silt and
Colluvial and alluvial deposits (Holo-
cene)--Areas of colluvium and alluvium
sand with some clay, cobbles, and boul-
too small to map separately. Chiefly moder-
ders, and a variable amount of organic
ately loose, sandy to rubbly diamicton,
material. Massive to poorly bedded; poorly
poorly sorted sand and gravel, and some
sorted. Generally a few meters thick, thin-
organic debris. Thickness probably a few
ner at the upslope part; usually thicker
meters. Contacts generally gradational.
downslope. Contacts generally well
Topography irregularly gullied, slopes
defined. Slopes steep to precipitous.
steep to very steep, generally ranging
Although stabilized locally by vegetation,
between 35 and 70%. Commonly covered
subject to instability because of renewed
by at least low vegetation, but vegetation
erosion and accompanying mass-wasting
may be lacking in some gullies where active
processes. Occur commonly along bluffs
deposition is occurring. Some instability of
developed in surficial deposits along Knik
slopes likely. Occur in small valleys and
Arm and along valley walls of major
gullies in mountains, especially near heads
streams where they cross the Anchorage
of small valleys.
Lowland. Locally present on scarps bor-
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