The California column consisted of approximately 2,000 troops. The troops came from volunteer regiments, along with parts of other regiments from the Army of the Pacific. The force was under the command of James H. Carleton, a Colonel in the United States Army. Under the orders of Brigadier-General George Wright, the Column's intended mission was to march from Los Angeles through Yuma and Tucson, in an effort to take back the Arizona Territory for the Union government. They were then to head on to New Mexico and expel the Confederates. The entire trek was to take place on the Overland Mail Route. They set out in early 1862 and made it to Yuma by April; entering Tucson in May(1).

Mr. Amni White had established a Flour Mill in the Pima Villages, and purchased crops from the Indians who were friendly with the Americans. This would allow the Union army to have supplies throughout their tenure in Arizona. The Confederates captured White and all his supplies were confiscated or destroyed.

Calloway heard reports of a Confederate force of about 500 in Tucson, so he decided to retreat back to the Pima Villages. Calloway encountered Lt. Col. West and decided to renew his march on Tucson, now that he had reinforcements. Carleton's plan was to capture Tucson, Hunter, and all the Confederate forces in tact. However, the battle at Picacho Pass destroyed the element of surprise.

On May 20, 1862 Captain Emil Fritz and his troops charged into Tucson from the west, while another company came from the east. The Union Armies discovered that the Confederates had already evacuated Tucson on May 14. The Union flag was raised over Tucson, while Hunter retreated back to the Rio Grande River.

Fort Breckenridge was also recovered by the Union troops during this excursion on May 21. The fort was re-christened Fort Sanford in honor of the Governor of California.

The California Column had driven the Confederates out of the Arizona Territory.