Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

contact of two Quaternary gravels (Qn and Qna) according to Scott and others (1975) and
is interpreted to be near the contact between Quaternary gravel (Qna) and the Tertiary
Dry Union Formation (Td) in this study. Smaller placer workings are present at the
junction of Placer Creek with Blank Gulch in the NE 1 / 4 of the NE 1 / 4 , Section 26 (Parker,
1974; and Scott and others, 1975).
A third area of placer workings was found during this study in the SE1/4, NW14,
Section 18, T50N, R8E. Abundant placer cuts explore the basal contact of the Quaternary
gravel (Qna) capping the Dry Union Formation (Td). Scott and others (1975) interpreted
the Quaternary gravel cap as Pleistocene Kansan () alluvium (Qk), whereas it is
interpreted to be Pleistocene Nebraskan alluvium (Qna) in this study. The placer
workings occur for a distance of 600 to 700 ft on the north and south sides of Droney
Gulch. The gravel cap consists of matrix supported boulder conglomerate with
subangular to rounded blocks to 5 ft in size. The gravel is bedded with sandy to gritty
layers and local imbrication of elongated conglomerate clasts. The gravel is distinctly
orange stained and locally the sand and conglomerate beds are irregularly impregnated
with weak Fe and Mn oxides. A small outcrop at creek level, interpreted to be in the
underlying Dry Union Formation, has bedded siltstone with a gritty, pebble conglomerate
layer containing moderate Fe and Mn oxides with a trace of Cu oxides on Proterozoic
pebble clasts. The placer workings are along the basal contact of the gravel cap with the
underlying Dry Union Formation. Parker (1974) indicated that about $30,000 in gold was
produced from the Section 15 placer area and that the gold is reported to have been heavy
and rough and was associated with abundant black sand in the gravel.
Parker (1974) concluded that most of the important placer deposits in Colorado
were formed during the Bull Lake or Pinedale stadials of the Wisconsin stage. Many of
the alluvial placers have been modified by glacial action. Glacial modification of
preexisting placers resulted in the formation of distinctive deposits that are localized in
the end and lower lateral moraines and in the outwash trains. He suggested that the source
of the placers in the Maysville quadrangle is the mineralized area high on the southeast
face of Mount Shavano where there was some eluvial placers.
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