Set of 50 stereoviews documenting the Wheeler Expeditions of 1871-1874, as photographed by Timothy H. O'Sullivan and William Bell. Numbered 1-50 on 4 x 7 in. mounts with the year of the expedition and "1st Lieut. Geo. M. Wheeler, Corps of Engineers Commanding," imprinted on recto, and on verso "War Department, Corp of Engineers, U.S.A. / Geographical Explorations and Surveys West of the 100th Meridian," followed by a specific description of each view and photo credit to either O'Sullivan or Bell. 

In 1869, Lt. George M. Wheeler led an exploratory expedition into California, Nevada, and Arizona, to map the landscape, record possible roadways, note native inhabitants, and consider sites for future military posts. On his return east in 1871, Wheeler proposed to survey and create a detailed map of the United States west of the 100th meridian, with a price tag of $2.5 million dollars and a time frame of 15 years, which Congress approved on 10 June 1872.

The official photographers for the Wheeler Survey were Timothy H. O’Sullivan (1840-1882), who had been a photographer for Mathew Brady and Alexander Gardner during the Civil War, and William Bell (1830-1910), who had documented Civil War combat injuries and diseases for the Army Medical Museum. Equipped with stereograph cameras, glass plates, darkroom equipment, and processing chemicals, they captured the mystic, unknown, western landscape. Many of their photographs were the very first of their particular subjects.