Rancho Atascadero was a 4,348-acre (17.60 km²) Mexican land grant in present-day San Luis Obispo County, California.

It was granted in 1842 by Governor Juan Alvarado to Trifon Garcia.^[1] The grant extended along the Salinas River and encompassed present-day Atascadero.^[2][3]

The one square league grant was from the secularized holdings of Mission San Miguel Arcángel. Trifon Garcia was a son of Ynocente Garcia, who was administrator at Mission San Miguel.^[4]

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 Atascadero was filed with the Public Land Commission in 1852,^[5][6] and the grant was patented to Henry Haight in 1860.^[7] A second claim was filed by Maria Antonia Ortega in 1853, but was rejected by the Commission due to lack of evidence of a grant.^[8]

The rancho was sold in 1864 to Martin Murphy Jr. (1807–1884) and his wife Mary Bulger Murphy (d.1892) of Sunnyvale, who had come to California with the Stephens-Townsend-Murphy Party in 1844.^[9][10] The Murphys turned over running of the rancho to their son Patrick Murphy, who was a General in the California National Guard.^{[11] [12]} Patrick Washington Murphy (1840–1901) operated Rancho Atascadero, and the adjacent Rancho Asuncion, and Rancho Santa Margarita, altogether comprising about 61,000 acres (247 km²), from his Rancho Santa Margarita headquarters.

In 1912, Edward Gardner Lewis, a successful magazine publisher, bought Rancho Atascadero from J.H. Henry. Lewis founded the utopian, planned community of Atascadero in 1913.^[13]

• Ranchos of San Luis Obispo County, California
• List of Ranchos of California