Template:Campaignbox Expedition from Camp Douglas, Utah, to Cache Valley, Idaho Template:Nineteenth century Asia/Pacific conflicts involving the United States The Pacific Coast Theater of the American Civil War was the military operations in the United States bordering or close to the Pacific Ocean. The theater was encompassed by the Department of the Pacific that included the states of California, Oregon, and Nevada, Washington Territory, Utah Territory, and later Idaho Territory. The operations of Union volunteer troop detachments primarily from California, some from Oregon and a few companies from Washington Territory were directed mostly against Indians in the theater. Union and Confederate regular forces did not meet directly within the Pacific Department but operations were directed against Confederate irregulars in California and strong garrisons were placed in Southern California to control the region which had strong secessionist sympathies. Though the Union and confederate armies did not meet, Confederate States Navy warships would operate along the Pacific/American coast, ultimately firing the last shot of the American Civil War in the Bering Sea off Alaska. Attempts by the Confederacy to buy or seize ships for commerce raiding on the West Coast were thwarted by alert Union officials.
The campaign classification established by the United States National Park Service lists only one campaign and one battle in this theater, the Battle of Bear River. However this is not correct, there were several campaigns against the Indian tribes besides the eastern Shoshone. In Northern California there was the ongoing Bald Hills War (1858–1864) against the Wiyot, Yurok, Karuk, Hupa, Tsnungwe, and Whilkut. From December 12, 1861 the theater of this war was made into the District of Humboldt with its headquarters at Fort Humboldt). It was a protracted irregular war requiring garrisons protecting settlements and long patrols sometimes resulting in small skirmishes.
In September 25, 1861 the District of Southern California was established, with its first Headquarters at Camp Latham, west of Los Angeles this was later moved to Drum Barracks. It was first formed to control what was seen as the secessionist majority population in Southern California. This district included Tulare County to the north which at the time was much larger than it is now including what is now Kings, Kern and Inyo Counties and part of Fresno County. In early 1862, the District headquarters was used as the base for the campaign of the California Column into Confederate Arizona. California sent some of their Volunteer Regiments east to clear the Confederate garrison from southern New Mexico Territory. Subsequently, California units remained there fighting the Navajo and the Apache Wars until after the Civil War when they were relieved by Federal Troops in 1866. In March 1865, Arizona Territory under the military District of Arizona, was transferred from the Department of New Mexico to the Department of the Pacific and in July 1865 to the Department of California. Between 1862 and 1864, Cavalry units from the Southern Califoria District fought the Owens Valley Indian War  against the Owens Valley Paiutes or Numa and against their friends among the Kawaiisu in the Sierra Mountains to the west.
Throughout the Civil War, Oregon and California Volunteer patrols had several clashes with the Ute, Paiute, Bannock, and Shoshone bands in Oregon and the Territories of Washington (later Idaho), Utah, and Nevada collectively known as the Snake Indians. However the invasion of Snake Indians territory by gold miners in 1863 brought on the Snake War. The Volunteers fought the Snakes until relieved by Federal troops in late 1865, the war continued until 1868.
Other operations west of the Mississippi River are included in the Trans-Mississippi Theater.
- California in the American Civil War
- Oregon in the American Civil War
- Washington Territory in the American Civil War
- Idaho in the American Civil War
- Montana in the American Civil War
- Utah Territory in the American Civil War
- Utah in the American Civil War
- Nevada in the American Civil War
- New Mexico Territory in the American Civil War
- Arizona Territory in the American Civil War
- The Bear River Massacre was formally in Washington Territory, which was partitioned into the Idaho Territory subsequent to the battle. However Col. Connor had the Bear River valley reassigned to his military District of Utah prior to his campaign to protect a settlement of Mormons there.Template:Reference necessary
- U.S. National Park Service, Civil War Battle Studies by Campaign
- The California State Military Museum, Historic California Posts: Camp Latham
- Historic California Posts: Drum Barracks (Camp San Pedro, Camp Drum, Fort Drum, and Wilmington Depot)
- Historic California Posts: Fort MacArthur - Military Museum
- The California Military Museum; California and the Indian Wars, The Owens Valley Indian War, 1861-1865.
fr:Théâtre de la côte pacifique de la Guerre de Sécession ja:太平洋岸戦線 (南北戦争) ru:Тихоокеанский театр военных действий Гражданской войны в США