Stanwix Station, in western Arizona, was a stop on the Butterfield Overland Stagecoach line built in the 1850s near the Gila River about 80 miles east of Yuma, Arizona. The station was the site of the westernmost engagement between Union and Confederate troops during the American Civil War.
The encounter took place on March 30, 1862, when Capt. William P. Calloway and a vanguard of 272 troops from the California Column discovered a small detachment of Confederates led by 2nd Lt. John W. Swilling burning hay, which had been placed at Stanwix Station for the California Column's animals. After a brief exchange of gun fire with the much larger Union force, the Confederates retreated to Tucson, the capital of the western district of the Confederate Territory of Arizona. The skirmish resulted in the wounding of a German born Union private named William Semmilrogge, who subsequently recovered. There appear to have been no other casualties.
The significance of the incident was two fold. First, the burning of hay, not only at Stanwix but at other former stagecoach stations, considerably slowed the California Column's advance and prevented them from reaching Mesilla, the territorial capital of Confederate Arizona, before the Confederates had evacuated almost all of their forces and removed or destroyed their supplies. Secondly, and of more immediate importance, Swilling was able to reach Tucson and warn Capt. Sherrod Hunter, district military commander of western Confederate Arizona, of the approaching California Column. This led Hunter to place pickets at strategic locations, leading to the Battle of Picacho Pass, where ten Confederate pickets were attacked by a Union cavalry detachment of about twelve. This "battle" was also only a skirmish, distinguished from the Stanwix Station fight simply by the comparatively more severe casualties (three dead and three wounded Union soldiers).