▁two ▁major ▁eth nic ▁groups ▁were ▁the ▁Mi w ok ▁people , ▁who ▁inhab ited ▁the ▁northern ▁end ▁of ▁the ▁San ▁Jo aqu in ▁Valley ▁and ▁the ▁Sac r amento - San ▁Jo aqu in ▁D elta ▁region , ▁and ▁the ▁Y ok uts ▁tribes , ▁scattered ▁around ▁the ▁more ▁ar id ▁southern ▁portion ▁of ▁the ▁bas in . ▁During ▁these ▁pre - Europe an ▁times , ▁the ▁San ▁Jo aqu in ▁River ▁flow ed ▁through ▁rich ▁grass lands ▁and ▁spraw ling ▁mar sh es , ▁flo oding ▁every ▁few ▁years ▁and ▁transform ing ▁much ▁of ▁the ▁valley ▁into ▁la kes . ▁At ▁the ▁southern ▁end ▁of ▁the ▁valley ▁lay ▁the ▁vast ▁Tul are ▁Lake , ▁formerly ▁the ▁largest ▁fresh water ▁lake ▁in ▁the ▁western ▁United ▁States , ▁which ▁connected ▁with ▁the ▁San ▁Jo aqu in ▁through ▁a ▁series ▁of ▁mar sh es ▁and ▁sl ough s . ▁The ▁rich ▁veget ation ▁and ▁wild life ▁surrounding ▁these ▁bodies ▁of ▁water ▁made ▁the ▁San ▁Jo aqu in ▁Valley ▁a ▁fav ored ▁home ▁as ▁well ▁as ▁a ▁stopping - off ▁place ▁for ▁other ▁nom adic ▁pe op les . ▁The ▁native ▁people , ▁mostly ▁h unter - g ather ers , ▁lived ▁off ▁this ▁land ▁of ▁abund ance ; ▁during ▁the ▁ 1 8 th ▁century , ▁the ▁population ▁of ▁the ▁San ▁Jo aqu in ▁Valley ▁was ▁estimated ▁at ▁more ▁than ▁ 6 9 , 0 0 0 , ▁representing ▁one ▁of ▁the ▁greatest ▁concentr ations ▁of ▁native ▁people ▁anywhere ▁in ▁North ▁America . ▁