The specific date of the battle of Picacho Pass is debatable. There is conflicting information as to when it happened. The confrontation either occurred on April 15, or April 16. Captain Calloway, of the Union army claims April 15, while Captain Hunter of the Confederate army, documented the date as April 16. The National Archives use Hunter's date, while other reputable sources use Calloway's. Captain Hunter was known for his record keeping, which gives weight to his claim of April 16. The battle itself consisted of only 24 troops: 14 Union under the command of Lieutenant James Barrett and 10 Rebel troops led by Sergeant Henry Holmes.

Hunter knew of Federal forces traveling up the Gila River, so he had Holmes stationed at the base of Picacho Peak to scout for these soldiers. Calloway was warned of this, so he sent out two cavalries to surround the pass. Lieutenant Barrett and Lieutenant Ephraim Baldwin led these units. Calloway planned to advance his men and capture the Rebel soldiers. He did not want a fight, because he needed to uncover information from the enemy troops. Calloway needed to know the situation in Tucson: how many troops there were, how fortified it was, etc.

The impulsive Barrett moved into the situation without waiting for word that the other units were in place.

"Reports state that Barrett and his thirteen troops could have captured the Confederates, but instead, 'led his men (including his scout) into the thicket single file without dismounting them, after having been requested twice by Mr. Jones (a scout) to do so.'(1)"

The Confederates shot first and "emptied four saddles.i" These men were more likely thrown from their untrained horses that became scared by the gunfire then actually shot. With the Union unit confused and disorganized, the Confederates regrouped and fortified their position. The battle raged for approximately an hour and a half. The fighting was very fierce. Union soldiers captured three prisoners: Sergeant Henry Holmes, William Dwyer, and John Hill. They also suffered some casualties during the battle that ensued, including the death of Lieutenant Barrett. Private George Johnson also died during the battle, and four others were injured: William Johnson (who died shortly after the battle), William Tobin, Peter Gann and James Botsford. The Rebels suffered no casualties during the clash, sans the three prisoners.