1. Maps showing mines, prospects, and areas of significant silver, lead, and zinc production in the Aspen quadrangle, Pitkin County, Colorado [cartographic material] Yale Public content 1972. 2013-04-17T19:33:50Z. 2013-05-02T15:44:45Z. Bryant, Bruce, 1930-. U.S. Geological Survey. English. Public. Colorado and Pitkin County.