Park Range and Rabbit Ears Range
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.
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
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.