The rancho took its name from the Ohlone village of Posolmi. Yñigo, an alcalde at Mission Santa Clara, was one of the few native Californians granted a rancho, and he kept more than 800 acres until his death in 1864.
In 1931 1,000 acres of the old rancho, bought by Bay Area communities, were sold to the Navy for $1 to become the airship base.