Geologic map of the Eagle quadrangle, Eagle County, Colorado

This map was funded by the National Cooperative Geologic Program as part of the
geologic mapping studies conducted along the I-70 urban corridor. This
corridor is experiencing rapid urban growth and geologic mapping is needed to
aid in land-use planning in order to address, avoid, and mitigate known and
potential geologic hazards.

The Eagle quadrangle covers an area that straddles the Eagle River and
Interstate 70 (I-70) and it includes the town of Eagle, Colo., which is located
in the southwestern part of the quadrangle, just south of I-70 and the Eagle
River, about 37 km west of Vail, Colo. The map area is part of the I-70 urban
corridor, which is experiencing rapid and escalating urban growth. Geologic
mapping along this corridor is needed for ongoing land-use planning. A variety
of rocks and deposits characterize the map area and areas nearby. Sedimentary
rocks present in the map area range in age from Pennsylvanian rocks, which were
deposited in the ancestral Eagle basin during the formation of the ancestral
Rocky Mountains, to Late Cretaceous rocks that were deposited just prior to the
formation of the present Rocky Mountains. The Pennsylvanian rocks in the map
area include a thick sequence of evaporitic rocks (Eagle Valley Evaporite).
These evaporitic rocks are commonly complexly folded throughout the southern
part of the quadrangle where they are exposed. In general, in the central and
northern parts of the quadrangle, the sedimentary rocks overlying the evaporite
dip gently to moderately northward. Consequently, the youngest sedimentary
rocks (Late Cretaceous rocks) are exposed dipping gently to the north in the
northern part of the quadrangle; landslide complexes are widespread along the
northerly dipping, dip slopes in shaly rocks of the Cretaceous sequence in the
northeastern part of the map area. During the Early Miocene, basaltic
volcanism formed extensive basaltic flows that mantled the previously deformed
and eroded sedimentary rocks. Erosional remnants of the basaltic flows are
preserved in the southeastern, west-central, and north-central parts of the map
area. Some of these basaltic flows are faulted and downdropped in a manner
that suggests they were downdropped in areas where large volumes of the
underlying evaporitic rocks were removed from the subsurface, beneath the
basaltic rocks, by dissolution or flowage of the evaporite in the subsurface.
Quaternary and late Tertiary(?) surficial deposits in the map area consist
mainly of Quaternary alluvium and colluvium, late and middle Pleistocene
terrace gravels of the Eagle River, Miocene(?) gravel remnants of the ancestral
Eagle River and its tributaries, and Pleistocene to recent mass movement
deposits that include landslides and debris flows. Potential geologic hazards
in the map area include landslides, debris flows, rockfalls, local flooding,
ground subsidence, and expansive and corrosive soils.

Map political location: Eagle County, Colorado
Compilation scale: 1:24,000
Geology mapped in 1997.

GEOSPATIAL DATA FILES INCLUDED IN THIS DATA SET:
eaglepy: polygon coverage containing geologic unit contacts and labels.
eagleln: arc coverage containing fold axes and other line entities.
eaglept: point coverage containing bedding attitude measurements
and other point entities.
eaglepit: polygon coverage containing gravel pits.