to low-lying, nearly flat channels, and in a
separately. Mapped mainly along major
few other localities where minor streams
streams; occur also along small streams in
cross areas of substantially lower slope
areas too narrow to map separately. alu are
deposits modified by urbanization.
than areas just upstream.
alf
afo
Fine-grained deposits along some minor
Older alluvial-fan deposits, undivided
alfu
afou
(Holocene and late Pleistocene)--Gravel
streams--Chiefly silt and fine sand; may
include some peat deposits near surface.
and sand, possibly admixed with some
Occur mainly along parts of Mink and Fire
finer-grained material and thin diamicton
Creeks and the Otter-Sixmile channel, and
beds. Deposits typically less well sorted
locally where small low-gradient streams
and more steeply sloping than those in
cross low-lying areas. alfu are deposits
other alluvial units. Occur commonly as
modified by urbanization.
remnants associated with younger alluvial
at
fans, but graded to levels well above mod-
Older alluvial deposits in terraces (Holo-
cene)--Chiefly gravel and sand, commonly
ern streams. Near mouth of Clunie Creek
several meters above stream level. Occur
represent slightly older part of main fan.
locally along Clunie Creek and Eagle River.
Common on lower parts of mountain-
ath
valley walls and present at a few places
Deposits in higher terraces (Holocene and
late Pleistocene)--Still older alluvium
along Chugach Mountain Front. afou are
occurring in local remnants about 10 m
deposits modified by urbanization.
above Meadow Creek and at least 5 m
Deposits along Peters Creek--Chiefly
afp
above the lower reaches of Eagle River.
afpu gravel with some sand. May be fan delta
alo
graded to a level above present sea level,
Older alluvial deposits in channels (Holo-
cene and late Pleistocene)--Chiefly gravel
and possibly latest Pleistocene in age; alter-
and sand in channels abandoned by
natively, might have extended substan-
stream that formed them and that are now
tially farther northwest into Knik Arm,
occupied, if at all, by underfit streams.
and be graded to near present sea level but
Thickness probably only 1 m to a few
eroded to present distribution. Slopes very
meters. Mapped only in a few places along
to moderately gentle, gradually increasing
tributaries to Ship Creek and in the Hill-
to steep near head of fan. Much material
side area between North and South Forks
removed as major source of gravel and
sand, especially near toe of fan. afpu are
of Campbell Creek.
deposits modified by urbanization.
Alluvial-fan deposits. These formed near the
Colluvial deposits
mouths of large streams and where small tribu-
The term colluvial deposits (colluvium), as used
tary streams enter larger streams that have lower
gradients. They are graded to or just above mod-
here, includes those deposits that occur on slopes
ern stream levels. Slopes are moderately gentle to
and that have accumulated primarily through the
moderate, steeper near the heads of fans.
action of gravity and, secondarily, through the
action of running water. Colluvium is broadly
af
subdivided into 1) deposits that have accumulat-
Coarse-grained
deposits
(Holocene)--
afu
Chiefly gravel and sand; dominantly gravel
ed particle by particle over a long period of time,
and 2) those deposits that have moved en masse.
in large fan near mouth of Peters Creek
Among those in category 1 are deposits on moun-
and possibly in large fan near mouth of
tain slopes, deposits derived mainly from mor-
Clunie Creek and where Eagle River enters
aines, and deposits on bluffs along streams and
Eagle River Flats; in moderate to small fans
along Knik Arm. Those in category 2 include both
common in many valleys may be some-
slow-moving solifluction deposits as well as a
what less well sorted than other alluvium,
and locally include silt and diamicton beds
variety of landslide deposits, most of which have
resulting from minor mudflows. afu are
been emplaced rapidly. Most colluvial deposits
deposits modified by urbanization.
are relatively poorly sorted and many are not
aff
Fine-grained deposits (Holocene)--Chiefly
well compacted; because of their location on
fine sand and silt; locally may include
slopes, they are subject to instability especially
coarser sand and some gravel. Occur mar-
when excavated.
ginal to intertidal deposits, in and adjacent
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