1857 seems about right.  Bandini was the sucessful claimant in 1855 (Land Case 213 SD), and died in 1859.  1841 was when Stearns married Arcadia Bandini. Boyd's "History of San Bernardino and Riverside counties"  mentions Rancho Jurupa and Williams and Colonel Johnson.  Hoover's "Historic spots in California" has Robidoux buying 1/2 interest from Wilson in 1848 and 1/2 interest from Williams in 1849.