The Geological Exploration of the Fortieth Parallel was a geological survey made by order of the Secretary of War according to acts of Congress of March 2, 1867, and March 3, 1869, under the direction of Brig. and Bvt. Major General A. A. Humphreys, Chief of Engineers, by Clarence King, U. S. geologist.[2] More commonly known as the Fortieth Parallel Survey, the survey conducted field work from 1867 to 1872, exploring the area along the fortieth parallel north from northeastern California, through Nevada, to eastern Wyoming.
- ^ "American West Photographs". National Archives and Records Administration. Retrieved 2008-03-23.
- ^ "Catalogue and Index of the Publications of the Hayden, King, Powell, and Wheeler Surveys" (PDF). United States Geological Survey. Retrieved 2011-07-20.