Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

1974). They are present in three zones in the eastern part of the graben. The eastern zone
(in the Salida West and Poncha Pass quadrangles) and the central zone (in the Salida
West, Maysville, and Mount Ouray quadrangles) were identified and described by
Russell (1950) and Van Alstine (1970). A third zone (western zone) of detached landslide
blocks that lies to the west of the two previously recognized zones (plates 1 and 3) was
identified in the Maysville quadrangle during this study.
The central zone has the best exposures and the most complete section of
Paleozoic sedimentary rocks. The largest and best exposure is at Elephant Rock (named
by Kansas State University students) just outside the western boundary of the Maysville
quadrangle. Van Alstine (1970) detailed descriptions of the landslide blocks are excellent
and can hardly be improved upon here. He described an about 300 ft thick section
including the Manitou, Harding, Fremont, and Chaffee Formations in the Elephant Rock
area. The Paleozoic blocks are made up predominantly of crackled and brecciated
dolomite and limestone with predominantly angular fragments set in a highly indurated
matrix of crushed carbonate rock cemented by fine to coarsely crystalline calcite.
Observations made during this study indicate that in terms of length to thickness
aspect most of the outcrops of Paleozoic rocks are more aptly described as landslide
sheets. The landslide sheets typically display coherent large-scale bedding features
between the different carbonate formations and especially between interlayered
brecciated carbonate and unbrecciated quartzite beds. The carbonates beds are
preferentially brecciated in comparison to the quartzite beds. The degree of brecciation of
carbonate beds is variable and there are wide variations in breccia textures including clast
size, clast-size sorting, degree of disruption of internal bedding, presence of chert
nodules, amount of carbonate cement, and clast to matrix relationships (fig. 18). The
horizons of sheets are characterized by lateral zones of small to large block conglomerate
that were emplaced at the same time. These lateral horizons of landslide blocks include
large blocks up to 10 to 12 ft in size of both brecciated and unbrecciated Paleozoic
carbonate rocks, unbrecciated Paleozoic quartzite and Proterozoic rocks, and a smaller
component of unbrecciated Tertiary volcanic rocks including welded ash-flow tuff.
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