Mount Oso is the site where the first State operated fire lookout station was constructed. Unfortunately, the original structure (built here in 1921 with funds from the Stockmen's Protective Association of Alameda and San Joaquin counties) has long since been removed. This earlier fire lookout facility was closed in 1938 and for the next few years, a patrolman was used for fire detection coverage. In 1942 the second tower was erected and the site re-activated as a fixed point detection site.

The existing tower reportedly was a World War Two surplus Army observation tower which came from the Tracy Airport and was installed in 1979. It may be an Aermotor Company product. The cab has been modified to accept a catwalk and door, and replacement windows. A small mobile home (circa 1960s) serves as a residence. The construction date for the garage is unknown.

Mount Oso is a northwest tending ridge located on the west side of the San Joaquin Valley, in Stanislaus County. The area is covered in annual grasses with a scattering of oaks and juniper. There are numerous radio vaults and towers at this site. The site is not accessible to the public, being some 13 miles from paved road. (MVT 10/91)