Rancho Santa Ysabel was a 17,774-acre (7,193 ha) Mexican land grant in present-day San Luis Obispo County, California given in 1844 by Governor Manuel Micheltorena to Francisco Arce.
[3] 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.
[6] Arce sold parts of the rancho to Jeremiah Clark in 1853, to Manual Castro in 1855, to Theodoro Gonzales in 1859, and to Maurice Dore 1874.
Chauncey Hatch Phillips bought Rancho Santa Ysabel in 1886, and subdivided it to be sold as farm lots to individuals ready to settle in the area being opened up by the arrival of the railroad.
Chauncey Hatch Phillips (1837–1902) was a San Luis Obispo real estate developer who acquired, subdivided and sold a number of Mexican land grants.