2 volumes, comprising: text, small 4to; atlas, large folio. Text volume: 43 plates, mostly from photographs. Atlas: 27 chromolithograph plates (2 double-page); printed slip pasted on title-page. Original green cloth lettered in gilt.

FIRST EDITION of Spurr and Emmons's work that details the complex geological features of the Aspen area, including its Paleozoic rock formations, intricate fault networks, and significant mineral deposits. During their research, they noticed intense dynamic disturbances in the region, particularly on Aspen Mountain, which they found to exhibit greater geological complexity than any similarly sized area in Colorado at the time.