The initial part of the regiment (companies A through F) was organized and mustered into the army in Oregon from December 1861 to April 1862. In May 1862, it was sent into the Washington Territory to the Walla Walla country to protect immigrants and miners along the Salmon River. The 1st Oregon occupied Fort Walla Walla in June 1862 and sent out various expeditions over the next two years to fight the Snake Indians and other threats. Hence, the regiment was rarely intact as a single unit for much of the war. Several companies scattered to other frontier forts, including Fort Vancouver and Fort Dalles (see also The Dalles, Oregon) for detached duty such as constructing roads through the wilderness.