Acquisition of California after the Mexican War made the War Department responsible for the protection of the area. The gold rush influx of Americans into every corner of the state caused an intermittent conflict with the Indians. Soldiers, therefore, had to protect the newly-arrived whites from depredations by the "first Californians," but, in many instances, also had to protect the Indians from brutal and senseless attacks by the settlers. To accomplish these objectives the United States Army ultimately dotted California with military installations. The more permanent were usually along the coast, often on the site of a former Mexican facility. Posts were established in the mining country to protect the miners, and garrisons were posted along communication routes, especially at key mountain Ipasses, to protect the large traffic to and from the mines. Many of these establishments existed for only a short time and were built to fill a real or imagined need. When the emergency had passed, they were abandoned and their garrisons moved elsewhere.
Because the terms forts, camps, and barracks, are often used interchangeably to describe the same site. They are omitted on the map. Some installations were of limited significance and these have been omitted at the discretion of the authors. Nor have all of the names by which a facility was known been used. For example, Fort Rosecrans has had various names as well as many sub-forts or associated installations in the San Diego area such as Fort Stockton, Presidio of San Diego, Fort San Diego, Garrison at San Diego, San Diego Barracks, Mission of San Diego and Fort Pio Pico: Fort McDowell was Camp Reynolds (1863-66) and Post of Angel Island (1866-1900), and since 1900, Camp and Fort McDowell.
Among the military installations existing
for supply purposes the greatest concentration was, naturally,
at San Francisco. Camp Drum (or Drum
Barracks, Wilmington Depot, or Camp San Pedro) serviced the Los
Angeles area; Fort Rosecrans the San Diego area. Forts Bragg and
Humboldt performed similar duties along the north coast, while
Fort Gaston acted as a supply point
on the Colorado River. Fort Bidwell
was located to protect the strategic route into California from
the northeast and Fort Yuma performed
a similar function in the southeast corner of the state. Camp
Cajon and Fort Tejon existed to protect strategic passes. The
purpose of Fort Moore, Camp
Rancho del Jurupa, and the detachment at Rancho del Chino
was to prevent another Hispano uprising against American rule.
The remaining military installations in California, in most cases,
were located to deal with conflict with the Indians.