Rancho Suscol was an 84,000-acre (340 km2) Mexican land grant in present day Napa County, California and Solano County, California given in 1843 by governor Manuel Micheltorena to General Mariano Guadalupe Vallejo. In a significant land law decision, the land claim was rejected by the US Supreme Court in 1862. Rancho Suscol extended from Rancho Petaluma on the west, south down to the San Francisco Bay and Mare Island and Carquinez Strait, and then to Rancho Suisun on the east. It included present day cities of Vallejo and Benicia.
In 1835, the Mexican Government gave Mariano Guadalupe Vallejo control of some newly secularized land. The Rancho Nacional Suscol was a national ranch under his control, heavily stocked with cattle and horses. Aiding Vallejo in various battles in exchange for cattle and other goods, Patwin populated this land living along the banks of Suscol Creek.
In March, 1843 Vallejo paid the government $5,000 for the support of the governor's troops and in return he was granted the 18 leagues Rancho Suscol by Mexican governor Micheltorena. Vallejo also received a confirming document (later considered to be a forgery by the US Supreme Court) signed by Pio Pico in 1845.
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 required by the Land Act of 1851, a claim for Rancho Suscol was filed with the Public Land Commission in 1853. The land grant was confirmed by the Land Commission and on appeal by the District Court, but rejected by the US Supreme Court in 1862 on want of authority in the Mexican government to make it.