▁Jo aqu in ▁Valley ▁for ▁more ▁than ▁ 8 , 0 0 0 ▁years , ▁and ▁it ▁was ▁long ▁one ▁of ▁the ▁major ▁population ▁cent ers ▁of ▁pre - Col umb ian ▁California . ▁Starting ▁in ▁the ▁late ▁ 1 8 th ▁century , ▁success ive ▁waves ▁of ▁expl or ers ▁then ▁sett lers , ▁mainly ▁Spanish ▁and ▁American , ▁em igr ated ▁to ▁the ▁San ▁Jo aqu in ▁bas in , ▁first ▁explo iting ▁then ▁driving ▁out ▁the ▁ind igen ous ▁tribes . ▁The ▁new com ers ▁quickly ▁appropri ated ▁the ▁rich ▁natural ▁and ▁hydro logic ▁resources ▁of ▁the ▁waters hed ▁for ▁use ▁in ▁far ms ▁and ▁cities , ▁but ▁found ▁themselves ▁pl ag ued ▁by ▁flo od ▁and ▁dr ought . ▁Because ▁of ▁the ▁uniform ▁top ography ▁of ▁the ▁San ▁Jo aqu in ▁Valley , ▁flo ods ▁once ▁transformed ▁much ▁of ▁the ▁lower ▁river ▁into ▁a ▁huge ▁in land ▁sea . ▁ ▁In ▁the ▁ 2 0 th ▁century , ▁many ▁le ve es ▁and ▁d ams ▁were ▁built ▁on ▁the ▁San ▁Jo aqu in ▁and ▁all ▁of ▁its ▁major ▁trib ut aries . ▁These ▁engineering ▁works ▁changed ▁the ▁fl uct u ating ▁nature ▁of ▁the ▁river ▁forever , ▁and ▁cut ▁off ▁the ▁Tul are ▁Bas in ▁from ▁the ▁rest ▁of ▁the ▁San ▁Jo aqu in ▁waters hed . ▁Once ▁habitat ▁for ▁hundreds ▁of ▁thousands ▁of ▁sp aw ning ▁sal mon ▁and ▁millions ▁of ▁mig rat ory ▁birds , ▁today ▁the ▁river ▁is ▁subject ▁to ▁trem end ous ▁water - supp