Battle of Picacho Pass
1862 CE.
Shown on the map at 32.631°, -111.416°.
The Battle at Picacho, also known as the Battle of Picacho Peak, was an engagement of the American Civil War on April 15, 1862. The action occurred around Picacho Peak, 50 miles (80 km) 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 involving fatalities (though a skirmish known as the Battle of Stanwix Station was 40 miles further west and 80 miles from the California border in the direction of Fort Yuma).
Text from the Wikipedia article Battle of Picacho Pass, licensed CC BY-SA 4.0.