About 50 miles southwest of Denver, U.S. 285 crosses Kenosha Pass, which separates the watersheds of the North and South Forks of the South Platte River. From a parking lot at the pass, one is treated to a broad view of South Park, one of four intermountain basins that stretch through the Rockies of Central Colorado. Quilted with hay fields and cattle ranches, this scenic parkland attracts pronghorn, mule deer and wintering herds of elk; of course, it also attracts the predators that feed on them: coyotes, black bear and mountain lions.
The Continental Divide curves along the north edge of the basin, crossed by Hoosier Pass in its northwest corner. Somewhat lower but no less scenic, the Mosquito Range forms the west edge of South Park while the Platte River and Tarryall Mountains rise to the east. The South Fork of the South Platte receives tributaries from all of these highlands and flows southward across the basin; the rise of the volcanic Thirty-Nine Mile Range, during the Oligocene, closed off the south edge of the Park, forcing the river to angle southeastward (towards Pike's Peak) and then northeastward through the Front Range foothills. The North and South Forks join in these foothills before the South Platte rumbles onto the Piedmont in southwest Metro Denver.
The geology of South Park is complex, the result of Precambrian ranges rising through flat beds of Paleozoic and Mesozoic sediments and subsequent erosion by mountain glaciers and streams.
Red Hill, a long hogback of Jurassic and Cretaceous Rock, knifes through the center of the Park, separating Paleozoic bedrock to its west from late Mesozoic bedrock to its east; both have since been covered by erosional and volcanic debris, which nourish this magnificent grassland.
