The forest is located in the Rocky Mountains, straddling the continental divide in the Front Range west of Denver. It was established on July 1, 1908, by President Theodore Roosevelt and named for the Arapaho tribe of Native Americans which previously inhabited the Colorado Eastern Plains. The forest includes part of the high Rockies and river valleys in the upper watershed of the Colorado River and South Platte River. The forest is largely in Grand and Clear Creek counties, but spills over into neighboring (in descending order of land area) Gilpin, Park, Routt, Jackson, and Jefferson counties. There are local ranger district offices located in Granby and Idaho Springs.