MLA

Geographical Surveys West of the 100th Meridian (U.S.). Land classification map of part of south western Colorado [cartographic material] : atlas sheet No. 61 (D).. BRBL_00587. 1879. https://collections.library.yale.edu/catalog/15824427.

APA, 6th edition

Geographical Surveys West of the 100th Meridian (U.S.). (["BRBL_00587"])(1879)[Land classification map of part of south western Colorado [cartographic material] : atlas sheet No. 61 (D).]. https://collections.library.yale.edu/catalog/15824427.