Map of the gem and gem extension mines : Idaho Springs, Colorado.
MLA
Map of the Gem and Gem Extension Mines : Idaho Springs, Colorado. s.n., 189AD. https://collections.library.yale.edu/catalog/15818458.
APA, 6th edition
Map of the gem and gem extension mines : Idaho Springs, Colorado. (189 C.E.). [Maps]. s.n., https://collections.library.yale.edu/catalog/15818458.