▁which ▁were ▁only ▁suitable ▁for ▁pla cer ▁min ing . ▁Many ▁of ▁these ▁people ▁settled ▁in ▁the ▁San ▁Jo aqu in ▁Valley , ▁most ▁in ▁the ▁existing ▁towns ▁such ▁as ▁Stock ton , ▁F res no ▁and ▁B akers field ▁but ▁some ▁establish ing ▁new ▁settlement s . ▁These ▁included ▁San ▁Jo aqu in ▁City , ▁near ▁the ▁confl u ence ▁of ▁the ▁San ▁Jo aqu in ▁with ▁the ▁Stanis laus , ▁probably ▁the ▁largest ▁of ▁these ▁post - g old - r ush ▁bo om town s . ▁Est ab lished ▁in ▁ 1 8 5 1 , ▁the ▁town ▁maintained ▁considerable ▁size ▁until ▁ 1 8 8 0 , ▁when ▁trade ▁competition ▁from ▁nearby ▁Stock ton ▁caused ▁it ▁to ▁dimin ish . ▁Another ▁notable ▁but ▁much ▁smaller ▁settlement ▁was ▁Las ▁J unt as , ▁near ▁present - day ▁M end ota . ▁This ▁was ▁a ▁haven ▁for ▁crim inals ▁and ▁fug it ives , ▁and ▁was ▁frequ ented ▁by ▁the ▁inf am ous ▁band its ▁Jo aqu ín ▁Mur ri eta ▁and ▁Tib ur cio ▁V ás quez . ▁ ▁It ▁was ▁in ▁the ▁mid - 1 8 6 0 s ▁that ▁the ▁San ▁Jo aqu in ▁River ▁and ▁its ▁surr ounds ▁under w ent ▁the ▁greatest ▁change ▁they ▁had ▁seen ▁in ▁human ▁history : ▁the ▁introduction ▁of ▁ir rig ated ▁agricult ure . ▁As ▁early ▁as ▁ 1 8 6 3 , ▁small ▁ir rig ation ▁can als ▁were ▁built ▁in ▁the ▁Center ville ▁area , ▁sout heast ▁of ▁F