Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

oth rockfalls and debris flows. Axial gully is typically flanked by prominent debrisflow
levees. Unit typically lacks matrix material near the surface, but dissected talus
reveal significant matrix at depth. Limited surface vegetation indicates that unit no longer
routinely receives active deposition. Thickness is probably less than 15 ft. Older talus fan
areas may be subject to rockfall and debris flows in extreme precipitation events.
Qs Solifluction deposits (late Pleistocene and Holocene) – Angular to subrounded
pebbles, cobbles, and large boulders in a chiefly sandy matrix deposited in alpine and
sub-alpine basins. Mapped in only two locations above timberline southeast of Mount
Shavano. Solifluction deposits result from the slow downslope flow of surficial deposits
that are water saturated and subject to seasonal freezing. Frost creep and melt-water
transport are also important factors in the formation of these deposits. This type of slope
movement involves a slow, downslope plastic deformation of the soil and surficial
deposits. Deposits are characterized by hummocky terrain, ground cracks and fissures up
to several inches wide, and numerous seeps and springs. On open hillslopes solifluction
also may produce lobes or terracettes, with small ledges or benches up to about 5 ft high,
due to differential movement of surficial material. Average thickness is typically less
than about 16 ft. These deposits may be susceptible to future downslope movement and
shallow groundwater.
ALLUVIAL DEPOSITS – Silt, sand, and gravel in stream channels, flood plains,
terraces, small debris fans, and sheetwash areas. The topographic relationships between
the various terrace levels of the South Arkansas River, and with their associated
moraines, are shown in figure 9.
Qal Stream-channel, flood-plain, and low-terrace alluvium (Holocene) – Deposits
are mostly clast-supported, pebble, cobble, and locally boulder gravel in a sandy silt
matrix. The deposits are locally interbedded with and commonly overlain by sandy silt
and silty sand. Clasts are subangular to well rounded and are of varied lithologies
reflecting the diverse types of bedrock within their provenance. Unit includes modern
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