Geologic Map of the Vail West quadrangle, Eagle County, Colorado

This map was funded by and is a product of the National Cooperative Geologic
Mapping Program. This corridor is experiencing rapid urban growth. Geologic
mapping is needed to aid in land development planning in order to address,
avoid, or mitigate known and potential geologic hazards.

This new 1:24,000-scale geologic map of the Vail West 7.5' quadrangle, as part
of the USGS Western Colorado I-70 Corridor Cooperative Geologic Mapping
Project, provides new interpretations of the stratigraphy, structure, and
geologic hazards in the area on the southwest flank of the Gore Range.

Bedrock strata include Miocene tuffaceous sedimentary rocks, Mesozoic and upper
Paleozoic sedimentary rocks, and undivided Early(?) Proterozoic metasedimentary
and igneous rocks. Tuffaceous rocks are found in fault-tilted blocks. Only
small outliers of the Dakota Sandstone, Morrison Formation, Entrada Sandstone,
and Chinle Formation exist above the redbeds of the Permian-Pennsylvanian
Maroon Formation and Pennsylvanian Minturn Formation, which were derived during
erosion of the Ancestral Front Range east of the Gore fault zone. In the
southwestern area of the map, the proximal Minturn facies change to distal
Eagle Valley Formation and the Eagle Valley Evaporite basin facies. The Jacque
Mountain Limestone Member, previously defined as the top of the Minturn
Formation, cannot be traced to the facies change to the southwest. Abundant
surficial deposits include Pinedale and Bull Lake Tills, periglacial deposits,
earth-flow deposits, common diamicton deposits, common Quaternary landslide
deposits, and an extensive, possibly late Pliocene landslide deposit.
Landscaping has so extensively modified the land surface in the town of Vail
that a modified land-surface unit was created to represent the surface unit.

Laramide movement renewed activity along the Gore fault zone, producing a
series of northwest-trending open anticlines and synclines in Paleozoic and
Mesozoic strata, parallel to the trend of the fault zone. Tertiary
down-to-the-northeast normal faults are evident and are parallel to similar
faults in both the Gore Range and the Blue River valley to the northeast;
presumably these are related to extensional deformation that occurred during
formation of the northern end of the Rio Grande rift system in Colorado.

In the southwestern part of the map area, a diapiric(?) exposure of the Eagle
Valley Evaporite exists and chaotic faults and folds suggest extensive
dissolution and collapse of overlying bedrock, indicating the presence of a
geologic hazard. Quaternary landslides are common and indicate that landslide
hazards are widespread in the area, particularly where old slide deposits are
disturbed by construction. The late Pliocene(?) landslide that consists largely
of a smectitic upper Morrison Formation matrix and boulders of Dakota Sandstone
is readily reactivated. Debris flows are likely to invade low-standing areas
within the towns of Vail and West Vail where tributaries of Gore Creek issue
from the mountains on the north side of the valley.

DATASETS INCLUDED IN THIS GEOSPATIAL DATABASE:
> vwpoly: geologic polygons, contacts, faults, marker beds, and
intra-unit scarps
> vwline: fold axes, concealed linear features, limits of abundant
chert fragments in the Maroon Formation, and cross-section lines
> vwpoint: bedding and foliation attitudes, and miscellaneous point data