Rancho Simi, also known as Rancho San José de Nuestra Señora de Altagracia y Simí, was a 113,009-acre (457 km2) Spanish land grant in what is now eastern Ventura and western Los Angeles counties granted in 1795 to Santiago Pico, founder of the Pico family of California.

[1][2] The name derives from Shimiji, the name of a Chumash village in the Simi Valley for thousands of years before the Spanish arrival.

[1] José de la Guerra y Noriega, a Captain of the Santa Barbara Presidio, who had begun to acquire large amounts of land in California to raise cattle, purchased Rancho Simi from the Pico family in 1842.

[4] With the cession of California to the United States following the Mexican–American War, the 1848 Treaty of Guadalupe Hidalgo provided that the land grants would be honored.

As late as February 1877, Juan De la Guerra was reported in county newspapers to be preparing to plant walnuts in the Tapo, which appears to be the final mention of their farming in relation to the original Simí grant.