Twelve Union cavalry troopers and one scout Tucson resident John W. Jones, commanded by Lieutenant James Barrett of the 1st California Cavalry, were conducting a sweep of the Picacho Peak area, looking for Confederates reported to be nearby. The Arizona Confederates were commanded by Sergeant Henry Holmes. Barrett was under orders not to engage them, but to wait for the main column to come up. However, "Lt. Barrett acting alone rather than in concert, surprised the Rebels and should have captured them without firing a shot, if the thing had been conducted properly." Instead, in mid-afternoon the lieutenant "led his men into the thicket single file without dismounting them. The first fire from the enemy emptied four saddles, when the enemy retired farther into the dense thicket and had time to reload ... Barrrett followed them, calling on his men to follow him." Three of the Confederates surrendered. Barrett secured one of the prisoners and had just remounted his horse when a bullet struck him in the neck, killing him instantly. Fierce and confused fighting continued among the mesquite and arroyos for more than an hour, with two more Union fatalities and three troopers wounded. Exhausted and leaderless, the Californians broke off the fight and the Arizona Rangers, minus three who surrendered, mounted and carried warning of the approaching Union army to Tucson. Barrett's disobedience of orders had cost him his life and lost any chance of a Union surprise attack on Tucson.
The Union troops retreated to the Pima Indian Villages and hastily built Fort Barrett (named for the fallen officer) at White's Mill, waiting to gather resources to continue the advance. However, with no Confederate reinforcements available, Captain Sherod Hunter and his men withdrew as soon as the Column again advanced. The Union troops entered Tucson without any opposition.
The bodies of the two Union enlisted men killed at Picacho were later removed to the presidio in San Francisco, California. However, Lieutenant Barrett's grave, near the present railroad tracks, remains undisturbed and unmarked.∼served in 1st US Dragons 1854-1860