In addition to the major fields, dozens of minor auxiliary fields and airstrips were built, generally to provide more room for basic flight training, but also to support other operations. A few of these were designed as "fallback fields" for launching defensive operations in case of a Japanese invasion.
Most Army airfields were built with three runways in a triangle, with parking ramp areas adjacent to one runway. This triangular configuration allowed rapid construction, without regard to the direction of the prevailing winds. Navy fields were generally built with two runways in a cross, with a third runway intersecting the other two at an angle.
There were, of course, other designs, including single-runway fields. Most noteworthy were "landing mats," large concrete squares, hexagons and circles, which allowed takeoffs and landings in any direction.
Following the war, many bases and auxiliary fields were given to local governments or returned to service as municipal airports. Often, budget constraints caused the new owners to close or even remove the "extra" runways, retaining only those that faced into the prevailing winds. In at least one case (Orland), large portions of a landing mat were removed, leaving a conventional runway and ramp.
A few were sold or given back to private owners, generally to be returned to agricultural use, while a handful have become private airports. A number of fields were simply abandoned, due to their remote locations, and the remains of these can still be found, especially in the Mojave Desert.
The mission of Fourth Air Force was the air defense of the West Coast, operating two air defense wings in California (Los Angeles and San Francisco). It also provided operational training of newly formed groups and squadrons in combat aircraft prior to their deployment to overseas combat theaters. After April 1944, operational training was changed to replacement training of newly commissioned pilots in combat fighters from the AAF Training Command advanced flying schools.
Training Command airfields in California provided Primary, Basic and Advanced (both single and multi-engine) pilot training under the Army Air Force Flying Training Command. Mather AAF provided Navigator Training. Training Command also provided technical aircraft support training to both enlisted and officer personnel at aircraft delivery fields, operated by manufacturers such as North American, Douglas, Northrup, Lockheed and Consolidated Aircraft. Santa Ana AAB provided basic indoctrination training to new enlisted personnel and also pilot qualification screening for prospective air cadets.
Private flying schools operated under contract by Flying Training Command, providing primary pilot training to new air cadets. Although training was provided by civilian contractors and instruction was provided by civilian instructors, the schools were commanded by military personnel and were operated as a military base. These schools operated from early 1942 until being phased out in mid-1944. Graduates then advanced to regular Training Command flight schools for Basic and Advanced training.
Provided aircraft modification prior to overseas deployment and also depot-level repair and maintenance services. Technical Service Command also operated acceptance centers for newly manufactured aircraft in Southern California, then ATC Ferrying Command transferred the new aircraft to various airfields or modification centers prior to deployment to operational units.