Snowmass, Colorado. For other places with the same name, see Snowmass. Snowmass (sometimes known locally as Old Snowmass) is an unincorporated community and a U.S. Post Office located in Pitkin County, Colorado, United States. It is situated in the valley of the Roaring Fork River, near the mouth of Snowmass Creek along State Highway 82 between Aspen and Basalt.