Under Colonel Justus Steinberger, organization for a three-year regiment began on 19 October 1861, with recruiting taking place within the territory as well as California.

Company A, B, C and D were organized at Alcatraz Island, San Francisco, California, January to April, 1862.

They were used for the protection of miners and settlers, emigrant parties and other travellers along the roads from the east, and participated with the 1st Oregon Cavalry in expeditions against Shoshone, Snake, and other hostile Indian groups.

Originally being recruited for a two-year term, some of the men were leaving or reenlisting in early 1864.

Orders in March 1863 sent them to Fort Boise in Idaho Territory,[5] where they remained stationed during their service.

Company E Mustered in at Alcatraz, they were ordered on 19 October 1862 to Camp Lapwai (would fall within the bounds of the Idaho Territory when created the following March), near the Nez Perce Agency.

The pass safely made, Company I returned to Fort Boise, where it remained until its mustering out on 20 November 1865.