John Bautista Rogers Cooper traded Rancho Bolsa del Potrero y Moro Cojo in the northern Salinas Valley with Juan Bautista Alvarado for the Rancho El Sur where the state park is located today. When the Mexican government ceded California to the United States after the Mexican–American War, the Land Act of 1851 required grantees to provide proof of their title. Cooper filed a claim for Rancho El Sur with the Public Land Commission in 1852, and he received the legal land patent after years of litigation in 1866. Cooper's son John Bautista Henry Cooper built a home on the ranch in 1899, but died soon after. John B.H. Cooper's sister Francisca Guadalupe Amelia Cooper inherited the southern portion of the rancho. When she died, her two children Andrew J. and Francisca (known as Frances) Molera inherited the land, although they lived their adult lives in San Francisco.