[2] The grant was located along the Pacific coast, and encompassed present-day San Onofre State Beach and Camp Pendleton.

Pio Pico later lost the land in a horse bet with Jose Andres Sepulveda.

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.

When Forster died in 1882, his heirs sold the ranch to Irish immigrant James Flood who selected his friend Richard O'Neill to manage it.

In 1923, Jerome O'Neill and James Flood, Jr. formed a corporation to control the ranch now known as Rancho Santa Margarita.