1. Slope map of the Aspen quadrangle, Pitkin County, Colorado [cartographic material] Yale Public content 1972. 2013-04-17T20:05:47Z. 2013-05-02T15:44:46Z. Bryant, Bruce, 1930-. U.S. Geological Survey. English. Public. Colorado, Pitkin County, and Pitkin County (Colo.).