The Treaty of Guadalupe Hidalgo of 1848 ended the United States - Mexican War, and the Territory of Arizona was ceded to the United States. The Arizona Territory limits was enlarged with the Gadsden Purchase of 1854, ratified in 1856. This purchase included much of the area long dominated by the Apache. Subsequent efforts to effectively control and govern the Arizona Territory, and pacify the Apache, severely tested the economic and military resolve of the young Nation, especially soon after emerging from a costly and devastating Civil War.
An early introduction of Americans into the lower limits of the Territory along the San Pedro valley (the river runs from south to north} area came when the American Boundary Commission personnel commenced work at the confluence of the Gila and the Saldo (Salt) Rivers. Difficulty between United States and
Mexican negotiators in reaching consensus as to where the international boundary line should be, delayed establishing the permanent boundary line. Meanwhile American railroad interest had as their objective; the acquisition of additional Mexican territory for a more southerly transcontinental railroad route. This was accomplished with the Gadsden Purchase of 1854, ratified in 1856. The United States acquisition included the San Pedro River valley, and the domain of the Apache.
Major William Emory, reporting on the United States Mexican Boundary Survey 1857, wrote effusively that "Throughout the whole course of the San Pedro there are beautiful valleys susceptible of irrigation and capable of producing large crops of wheat, corn, cotton and grapes; there are on this river the remains of large settlements which have been destroyed by the hostile Indians...". Submitted to Congress July 29, 1856 P/94