Battle of Picacho Pass The Battle of Picacho Pass or the Battle of Picacho Peak was an engagement of the American Civil War on April 15 , 1862 . The action occurred all around Picacho Peak , northwest of Tucson , Arizona . It was fought between a Union cavalry patrol from California and a party of Confederate pickets from Tucson , and marks the westernmost battle of the American Civil War . Background . Due to perceived neglect by the Federal government , Confederate sympathies were high in Tucson among the southern - born Anglo - American population . The Confederates proclaimed Tucson the capital of the western district of the Confederate Arizona Territory , which comprised what is now southern Arizona and southern New Mexico . Mesilla , near Las Cruces , was both the territorial capital and seat of the eastern district of the territory . Confederate dreams included influencing sympathizers in southern California to join them and give the Confederacy an outlet on the Pacific Ocean . The Federal government was anxious to prevent this , and Union volunteers from California , known as the California Column and led by Colonel James Henry Carleton , moved east to occupy Arizona , using Fort Yuma , California , as a base of operations . Like most of the Civil War era engagements in Arizona ( Dragoon Springs , Stanwix Station , and Apache Pass ) Picacho Pass occurred near remount stations along the former Butterfield Overland Stagecoach route , which opened in 1859 and ceased operations when the war began . This skirmish occurred about one mile northwest of Pichaco Pass Station . Battle . Twelve Union cavalry troopers and one scout ( reported to be mountain man Pauline Weaver but in reality 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 90 minutes , 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 { George Johnson and William S Leonard } were later removed to the presidio in San Francisco , California . However , Lieutenant Barrett ' s grave , near the present railroad tracks , remains undisturbed and unmarked . Union reports claimed that two Confederates were wounded in the fight , but Captain Hunter in his official report mentioned no Confederate casualties other than the three men captured . Aftermath . A Confederate patrol had actually reached the California border during the foray to burn hay at the stage stations in order to delay the Union advance from California . However , the goal of expanding Confederate influence to the Pacific Ocean never materialized . About the same time as the skirmish at Picacho , a larger force of Confederates was thwarted in its attempt to advance northward from Santa Fe , New Mexico , in the Battle of Glorieta Pass . By July the Confederates had retreated to Texas , though pro - Confederate militia units operated in some areas until mid - 1863 . The following year , the Union organized its own territory of Arizona , dividing New Mexico along the state ' s current north - south border , extending control southwards from the provisional capital of Prescott . The encounter at Picacho Pass may have been only a minor event in the Civil War , but it can be considered the high - water mark of the Confederate West . Re - enactment . Every March , Picacho Peak State Park hosts a re - enactment of the Civil War battles of Arizona and New Mexico , including the battle of Picacho Pass . The re - enactments now have grown so large that many more participants tend to be involved than took part in the actual engagements , and include infantry units and artillery as well as cavalry .