Geologic map of the Vail East quadrangle, Eagle County, Colorado

New 1:24,000-scale geologic mapping along the Interstate-70
urban corridor in western Colorado, in support of the State/
USGS Cooperative Geologic Mapping Project, is contributing to a
more complete understanding of the stratigraphy, structure,
tectonic evolution, and hazard potential of this rapidly
developing region. The 1:24,000-scale Vail East quadrangle
straddles the Gore fault system, the western structural
boundary of the Gore Range. The Gore fault system is a
contractional structure that has been recurrently active since
at least the early Paleozoic and marks the approximate eastern
boundary of the Central Colorado trough, a thick late Paleozoic
depocenter into which thousands of meters of clastic sediment
were deposited from several uplifts, including the ancestral
Front Range. The Gore fault was active during both the late
Paleozoic and Upper Cretaceous-lower Tertiary (Laramide)
deformations. In addition, numerous north-northwest faults that
cut the crystalline rocks of the Gore Range were active during
at least 5 periods, the last of which was related to Neogene
uplift of the Gore Range and formation of the northern Rio
Grande rift.
Early Proterozoic crystalline rocks underlie the high Gore
Range, north and east of the Gore fault system. These rocks
consist predominantly of migmatitic biotite gneiss intruded by
mostly granitic rocks of the 1.667-1.750 Ma Cross Creek
batholith, part of the 1,667-1,750 Ma Routt Plutonic Suite (
Tweto, 1987).
Southwest of the Gore fault, a mostly gently south-dipping
sequence of Pennsylvanian Mimturn Formation, as thick as 1,900
m, and the Permian and Pennsylvanian Maroon Formation (only the
basal several hundred meters are exposed in the quadrangle)were
shed from the ancestral Front Range and overlie a thin sequence
of Devonian and Cambrian rocks. The Minturn Formation is a
sequence of interlayered pink, maroon, and gray conglomerate,
sandstone, shale, and marine limestone. The Maroon Formation
is mostly reddish conglomerate and sandstone.
Glacial till of both the middle Pleistocene Bull Lake and late
Pleistocene Pinedale glaciations are well exposed along parts
of the Gore Creek valley and its tributaries, although human
development has profoundly altered the outcrop patterns along
the Gore Creek valley bottom. Landslides, some of which are
currently active, are also mapped.