MLA

Bonsall, J. H. Map of Colorado, with Plans of Its Principal Towns / Compiled from Official Authorities by J.H. Bonsall and E.H. Kellogg. Bonsall and Kellogg, 1872. https://collections.library.yale.edu/catalog/15818409.

APA, 6th edition

Bonsall, J. H. (1872). Map of Colorado, with plans of its principal towns / compiled from official authorities by J.H. Bonsall and E.H. Kellogg. [Maps]. Bonsall and Kellogg, https://collections.library.yale.edu/catalog/15818409.