This large, colorful geological map is a product of Clarence King's monumental survey along the 40th Parallel. It is printed on two unjoined sheets, which if joined would measure approximately 42 x 29". Coloring and pattern are used to indicate eleven different eruptive rock types and 13 sedimentary divisions. Elevation is shown via contour lines. Beneath each map is a detailed elevation plan and cross-section of the terrain that uses the same color and pattern to show geological structure. Together the west and east sheets (Map IV) cover the region between 117° and a little east of 114°, and from below 40° North to about 41° 30' and locate Fort Ruby, Camp Halleck, Beachey's Station, Chimney Station, Mineral Hill, Custer Spring, Last Chance Spring, and more. The villages and settlements of Lucin, Montello, Independence, Tulasco, Tuscarora, Moleen, Palisade, and Be-o-wa-we are named. The locations of all-important springs are shown.

King was only 25 and a few years out of Yale when he was appointed Geologist in Charge of the Geological Exploration of the Fortieth Parallel. Earlier as a member of the Geological Survey of California he conceived the idea of a scientifically conducted geological survey along the route of the railroad then being built, which the War Department endorsed and funded. The survey party included two assistant geologists, three topographic aides, two collectors, a photographer, and other assistants. These two large maps detail a portion of their efforts.

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Condition: A

Printed on thick paper with a few marginal flaws, map is near fine.