Rancho Los Alamos
Rancho Los Alamos was a 48,803-acre (197.50 km2) Mexican land grant in present day Santa Barbara County, California given in 1839 by Governor Juan Alvarado to José Antonio de la Guerra, a son of José de la Guerra y Noriega. Los Alamos is Spanish for "the cottonwoods" and describes Fremont Cottonwood (Populus fremontii) trees lining the banks of the San Antonio Creek.
In 1839, during Mexico's rule of Alta California, Jose Antonio de la Guerra was granted title to Rancho Los Alamos in the Los Alamos Valley. Concepcion Ortega, who married Jose de la Guerra, came to live at the adobe ranch house.
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 Los Alamos was filed with the Public Land Commission in 1852, and the land grant was patented to de la Guerra in 1872.
In 1876, San Francisco financier Thomas Bell along with his son John S. Bell, and James B. Shaw, purchased acreage from Rancho Los Alamos and the neighboring Rancho La Laguna. Both families allocated a half square mile from each of their new ranches to create the Los Alamos town site with "Centennial Street" as the central thoroughfare. 
Historic sites of the Rancho
- Los Alamos Ranch House. A one story adobe ranch house established about 1840 and designated a National Historic Landmark in 1970.
- Ogden Hoffman, 1862, Reports of Land Cases Determined in the United States District Court for the Northern District of California, Numa Hubert, San Francisco
- Diseño del Rancho Los Alamos
- Los Alamos Valley History
- United States. District Court (California : Southern District) Land Case 83 SD
- Report of the Surveyor General 1844 - 1886
- Short History of Los Alamos
- Question: ‘What is the history of Los Alamos?’