Bordering the western side of North, Middle, and South Parks, another
long north-south trending ridge extends from the Wyoming border toward
the center of Colorado. The northern part of this ridge, forming the
western boundary of the main mountain mass in the state, is called the
Park Range.
The structure of the Park Range is similar to that of the Front Range: a
huge linear corrugation in the earth’s crust, bounded by faults. Because
this area has fewer resistant sedimentary rock layers above the
Precambrian basement rocks, it is not prominently edged with upturned
sedimentary layers.
[Illustration: Hahn’s Peak, a highly eroded laccolith of rhyolite
porphyry, lies on the west side of the Park Range, along the eastern
margin of the Plateau Province. Placer gold was discovered here in 1865,
but the bedrock source of the gold was never found. (Jack Rathbone
photo) A geologic section shows the structure of the area.]
TERTIARY
RED BEDS
JURASSIC
DAKOTA
MANCOS
DAKOTA
Hahn’s Peak
PORPHYRY
MANCOS
DAKOTA
PORPHYRY
JURASSIC
RED BEDS
RE-CAMBRIAN
[Illustration: Hahn’s Peak]
The range is crossed by Rabbit Ears Pass in the north; Gore Pass near
Kremmling marks its southern end. Mt. Zirkel (12,180 feet) and Flattop
Mountain (12,118 feet) are the two high points of the range; these and a
number of unnamed peaks over 11,000 feet high are upward-faulted blocks
of Precambrian granite.
A rough ridge of volcanic country joins the Park Range with the Front
Range and effectively separates North Park and Middle Park. This is the
Rabbit Ears Range, named for a double-eared knob of Precambrian granite
near Rabbit Ears Pass on U. S. highway 40. Many Tertiary volcanic
features, including dikes and lava flows, can be seen along this ridge,
which is also traversed by Colorado state highway 125 between Granby and
Walden via Willow Creek Pass.