Following the Gadsden Purchase, the United States Army sent Major Enoch Steen and four companies of the 1st U. S. Dragoons (now the 1st U. S. Cavalry) to occupy the former site of the Mexican Presidio de Calabasas.

With the coming of the American Civil War all military posts in western New Mexico Territory (now Arizona) were abandoned.

Old Camp Moore at Calabasas was briefly occupied by the Confederates in March 1862, just before the arrival of the California Column in April.

The California Volunteers posted troops at Tucson and Tubac, and established Fort Bowie.

[2][3] Camp Moore and Fort Mason were collocated south of the confluence of Potrero Creek and the Santa Cruz River.