[4][5] 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.
[8] In 1855 Flint, Bixby & Co bought the Rancho San Justo from Francisco Pérez Pacheco with the understanding that William Welles Hollister would buy a one-half interest in the ranch in 1857.
Rancho San Justo was held in joint custody for three years, until the property was divided in 1861.
Thomas Flint and Hollister dissolved their partnership, with Flint taking all the land east of the San Benito River, and Hollister the land west of the river.
Later, Hollister and Flint traded holdings, with Hollister taking the land east of the San Benito River, and Flint taking the land lying to the west, including the San Juan Valley.