Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

microcline, and muscovite. The latter crystal fragments are detrital contaminants from
Proterozoic rocks.
Figure 15. Subcrop of fissile volcanic ash bed (Td2v) in the Dry Union
Formation South Arkansas graben sequence.
The volcanic ash bed at the Section 7 locality is well exposed and was traced for
about 1,200 ft along strike (fig. 17). Discontinuous outcrop and subcrop indicate the ash
bed is about 3.0 to 3.5 ft thick. The map pattern has an overall strike of about N35°E with
a broad warping with the convex side to the west. Individual bedding orientations
indicate 25°to 37° dips mainly to the northwest, but dips locally change to the westsouthwest.
The orientation of the ash bed is parallel and conformable with bedding in the
surrounding Dry Union Formation siltstones, clay beds, and conglomerates. On the basis
of tephrochronological studies, Hubbard and others (2001) determined ages of 13.3 +/-
0.2 Ma and 14.2 +/- 1.4 Ma on two volcanic ash locations from this same general area.
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