Rancho Los Méganos was a 13,316-acre (53.89 km2) Mexican land grant in the southwestern Sacramento-San Joaquin Delta region of present-day Contra Costa County, California.

The Spanish and Mexican governments made many concessions and land grants in Alta California and Baja California from 1775 to 1846. The Spanish Concessions of land were made to retired soldiers as an inducement for them to settle in the frontier. These Concessions reverted to the Spanish crown upon the death of the recipient.