Rancho Petaluma was a 66,622-acre (269.61 km2) Mexican land grant in present-day Sonoma County, California given in 1834 by Governor José Figueroa to Mariano Guadalupe Vallejo.
[2][3] In 1833, Lieutenant Vallejo was ordered by Governor Figueroa to examine the country north of Mission San Rafael, and to visit Fort Ross and Bodega Bay.
Governor Figueroa gave Vallejo vastly increased powers; his title was Military Commander and Director of Colonization of the Northern Frontier, and he was specifically requested to take charge of the mission at Sonoma, reduce it to the status of a parish church, free the Indian workers, and distribute the mission lands and other assets among the population at large.
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.
In 1864, Vallejo sold the last remaining 1,450 acres (6 km2) of the original Rancho Petaluma to San Francisco banker Alfred Borel.