Rancho Vallecitos de San Marcos was a 8,975-acre (36.32 km2) Mexican land grant in present-day northern San Diego County, California, given in 1840 by Governor Juan Alvarado to Jose María Alvarado.
The grant was located between Rancho Rincon del Diablo of Alvarado's father, Juan Bautista Alvarado on the east and Rancho Buena Vista on the west, and encompassed present day San Marcos.
[2][3] José María Alvarado (1813–1846) and his wife María Lugarda Osuna were granted the two square league Rancho Vallecitos de San Marcos in 1840, but less than a year after taking possession, he sold the rancho to Lorenzo Soto.
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.
Tomas Alvarado sold Rancho Vallecitos de San Marcos to Cave Johnson Couts in 1866.