▁the ▁San ▁Jo aqu in ▁flow ed ▁freely ▁through ▁a ▁grass ▁and ▁mar sh - domin ated ▁region ▁various ly ▁known ▁as ▁the ▁" Cal iforn ia ▁pra irie ", ▁" Cal iforn ia ▁annual ▁grass land ", ▁or ▁" Cent ral ▁Valley ▁grass lands ". ▁It ▁is ▁widely ▁believed ▁that ▁the ▁dominant ▁grass ▁species ▁throughout ▁the ▁San ▁Jo aqu in ▁River ▁valley ▁and ▁Tul are ▁Bas in , ▁as ▁well ▁as ▁the ▁Sac r amento ▁Valley , ▁the ▁Sierra ▁fo oth ills ▁and ▁Coast ▁R anges , ▁was ▁N ass ella ▁pul ch ra , ▁a ▁type ▁of ▁bunch gr ass ▁more ▁commonly ▁known ▁as ▁pur ple ▁need le gr ass . ▁Today , ▁this ▁veget ation ▁community ▁exists ▁only ▁in ▁isolated ▁po ckets ▁because ▁of ▁development ▁of ▁the ▁valley ▁for ▁agricult ure , ▁and ▁in ▁much ▁of ▁the ▁rem nant ▁open ▁areas ▁where ▁it ▁once ▁th riv ed , ▁now ▁grows ▁introduced ▁fl ora ▁such ▁as ▁annual ▁r ye ▁and ▁wild ▁o at . ▁The ▁veget ation ▁communities ▁created ▁by ▁the ▁introduced ▁grass es ▁are ▁sometimes ▁referred ▁to ▁as ▁" val ley ▁grass land ", ▁which ▁is ▁highly ▁season al ▁but ▁is ▁spread ▁throughout ▁the ▁Central ▁Valley ▁from ▁near ▁Red ding ▁to ▁south ▁of ▁B akers field . ▁These ▁grass es ▁all ▁th rive ▁in ▁the ▁Mediter rane an ▁climate ▁that ▁domin ates ▁much ▁of ▁the ▁San ▁Jo aqu in ▁Valley . ▁ ▁The ▁San ▁Jo aqu in ▁River ▁and ▁its ▁mar sh es ▁and ▁wet lands ▁provide ▁a ▁critical ▁rest