Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

lines with ticks in direction of sliding). May be more than 33 ft thick.
Qlso Landslide deposits, older (middle to late Pleistocene) – Mapped on the south
valley wall of the South Arkansas River, both west and east of McClure Creek (fig. 10).
The latter landslide is a wedge failure of relatively intact Proterozoic rock, sliding
northward on the intersection between northwest- and northeast-striking normal faults.
As shown in figure 10, this landslide is the youngest, smallest, and lowest wedge failure
(Slide Block III) at the base of a large area of progressively larger, inferred bedrock
wedge failures (Slide Blocks I, II) that extend up to elevation 10,200 ft (those inferred
gravity slide blocks are not composed of rubbilized landslide deposits, so are mapped as
Proterozoic bedrock). The landslide mass may be more than 100 ft thick. Also mapped on
the west side of Lost Creek, where the failed source material is Dry Union Formation.
ALLUVIAL AND COLLUVIAL DEPOSITS – Gravel, sand, and silt deposited by
both alluvial and colluvial processes in debris fans, stream channels, flood plains, and
lower reaches of adjacent hillslopes. Depositional processes in stream channels and on
flood plains are primarily alluvial, whereas colluvial and sheetwash processes are
predominant on debris fans and along the hillslope-valley floor boundary.
Qac Alluvium and colluvium, undivided (late Pleistocene to Holocene) – A mixture
of alluvial deposits of ephemeral, intermittent, and small perennial streams, and of
colluvial deposits deposited from valley sides. Alluvium is typically composed of poorly
to well sorted, stratified, interbedded, pebbly sand, sandy silt, and sandy gravel.
Colluvium ranges from unsorted, clast-supported, pebble to boulder gravel in a sandy silt
matrix to relatively well-sorted sand composed of disintegrated granitic rocks (grus).
Clast lithologies vary and are dependent upon the bedrock or surficial unit from which
the deposit was derived. Mapped as long narrow deposits in the valley bottoms in most of
the drainages incised into the range-front piedmont north of the South Arkansas River.
Mapped at the head of Lost Creek (west-central quadrangle boundary), where deposit
occupies a large area shaped like an alluvial fan. Also mapped south of the South
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