This Library of Congress site links to Notes of a Military Reconnoissance [sic], From Fort Leavenworth, In Missouri, To San Diego, In California, Including Part of the Arkansas, Del Norte, and Gila Rivers. By W.H. Emory, Brevet Major, Corps Topographical Engineers. Made in 1846-7, with the Advanced Guard of the "Army of the West." (Washington, DC: Wendell and van Benthuysen, Printers, 1848).
This book, describing the area between Bent's Fort and California with full notes, astronomical readings and maps, possibly was the greatest single factor that led to the opening of the southern snowfree route to California. For just a year later the great gold rush started, and Emory's book brought travelers along the Gila in increasing numbers. - According to Amazing Arizona! Historical Markers in Arizona. (Phoenix, AZ: Arizona Development Board, )