1st Battalion California Volunteer Mountaineers was an infantry battalion in the Union Army during the American Civil War. It spent its entire term of service in the western United States, attached to the Department of the Pacific. It was organized from men from the counties of Humboldt, Mendocino, Trinity, Klamath, Siskiyou, and Del Norte, and other parts of California, between May 30, 1863, and March 16, 1864, for special service in the redwood forests and mountains that was being fought over in the Bald Hills War in Humboldt County within the Humboldt Military District. The Battalion mustered out June 14, 1865.