Rancho Cosumnes (also called "Rancho de Hartnell") was a 26,605-acre (107.67 km2) Mexican land grant in present-day Sacramento County, California given in 1844 by Governor Manuel Micheltorena to William Edward Petty Hartnell.
[2] William Edward (Guillermo Eduardo) Petty Hartnell (1798–1854) received the five square league Rancho Todos Santos y San Antonio in Santa Barbara County from Governor Juan B. Alvarado in 1841 and sold his Rancho El Alisal to Alvarado.
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.
The U.S. Supreme Court affirmed the decree,[5] and the grant was patented to William Edward Petty Hartnell in 1869.
Hartnell wrote in his will - "My principal object is to prevent any member of the law from having anything whatsover to do with my property or with my executors or heirs."