The Sitgreaves Expedition was a U.S. military exploration mission that took place in 1851. Led by Lieutenant Amiel W. Whipple, the expedition aimed to survey a route for a transcontinental railroad through the southwestern United States. The team traveled through areas that are now part of Arizona and New Mexico, documenting the geography and resources of the region. The expedition is named after Edward Sitgreaves, who was the chief of the U.S. Army Corps of Topographical Engineers at the time. Although the mission faced numerous challenges, including harsh weather and difficult terrain, it contributed valuable information about the area, influencing future exploration and settlement.