Geological Map of a Part of the State of California Explored in 1853 by Lieut. R.S. Williamson U.S. Top. Eng.r.

Single sheet (22 x 16 inches to the neat line). Fine engraved map of California from the border with Oregon Territory in the north to Cape St. Quentin in the south, lithographed by Sarony, Major & Knapp of New York after Williamson, with original hand-colour highlighting the different geological zones and key (original folds). From "Report of the Secretary of War communicating the Several Pacific Railroad Explorations" House of Representatives Executive Document 129, Washington, 1855, to accompany William P. Blake's "Report of a Geological Reconnoissance in California". The key lists nine geological zones mapped by Williamson including: Granitic and Metamorphic; Erupted Granite and Syenite; Serpentine, Trap, Greenstone and Porphyry; Basaltic Lava; Metamorphic Slates; White and chrystalline Limestone; Teptiary and Quaternary; Tertiary; and Alluvium. The map also shows some interesting details along the American River: a huge Mono Lake is shown, but not Lake Tahoe, which has in its place is a small lake named Lake Bonpland. In Southern California, Los Angeles, San Gabriel and San Pedro are shown. Howes W-504; Marcou & Marcou 678.…