Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

as at the mouth of Squaw Creek. However, it is difficult to measure the tectonic offset of
Quaternary deposits across these fault traces, for three reasons.
First, many of the faults coincide with the fronts of terminal moraines (for
example, Squaw Creek), so the vertical relief from recent faulting cannot be distinguished
from the primary vertical relief formed during moraine deposition. Second, across most
fault scarps different-age deposits are on the upthrown and downthrown sides,
complicating displacement estimates. Third, fault scarps are obscured in places by
landslides. These landslides may be earthquake-induced landslides and flowslides that
formed during the violent ground shaking and surface rupturing on the Shavano fault
zone, but the height of the present landslide headscarp almost certainly exaggerates the
amount of vertical fault surface displacement during each faulting event. Altogether, the
surface expression of Quaternary faulting on the Shavano fault zone is less well
preserved and less impressive than at range-front locations farther north, such as along
the Sawatch fault zone in the Buena Vista West quadrangle (McCalpin and Shannon,
2005).
Evidence for additional Quaternary faulting exists in the far northeastern corner of
the quadrangle (Sections 1, 2, 11, 12; T50N, R7E; and Sections 35, 36; T51N, R7E),
where a group of four suspected Quaternary faults cuts Tertiary Dry Union Formation.
These faults were identified from aligned, down-to-the-east steps in the Quaternary
pediment surfaces. These steps tend to be rather broad and 12 to 30 ft high, so if they are
fault scarps, they are more subdued (and presumably older) than fault scarps of the
Shavano fault zone. The faults appear to continue between several pediment surfaces and
are inferred to connect via prominent gullies on valley sidewalls. The overall strike of
these faults ranges from N15°W to N30°W. In addition, there is a parallel N30°Wtrending
lineament to the southwest of this fault swarm.
None of these faults were exposed in outcrop, so the latest period of movement is
unknown. They appear to dismember the east-sloping Nebraskan pediment surface (map
unit Qna), so some of the movement must predate the early Pleistocene.
If these faults are projected about 3 mi northward into the Mount Antero
quadrangle, they would intersect the southern end of the range-front Sawatch fault zone,
which north of Brown’s Creek trends about N20°W. South of that point, the range front
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