, ▁south , ▁and ▁west ▁sides , ▁with ▁juni per ▁and ▁st unted ▁fir ▁trees , ▁grass es , ▁and ▁s age br ush ▁the ▁dominant ▁plant ▁species . ▁The ▁south ▁side ▁of ▁Tower ▁Rock ▁ab uts ▁the ▁Missouri ▁River , ▁where ▁the ▁rock ▁face ▁is ▁almost ▁vertical . ▁ ▁History ▁of ▁Tower ▁Rock ▁ ▁Native ▁Americans ▁and ▁Lewis ▁and ▁Clark ▁Tow ard ▁the ▁end ▁of ▁the ▁last ▁gla cial ▁period , ▁Tower ▁Rock ▁became ▁in und ated . ▁The ▁P ined ale ▁Gla ci ation ▁( an ▁ice ▁sheet ▁formed ▁from ▁gla ci ers ▁origin ating ▁in ▁the ▁Rock y ▁Mountains ) ▁and ▁the ▁Laurent ide ▁Ice ▁She et ▁( an ▁ice ▁sheet ▁which ▁covered ▁the ▁Great ▁Pla ins ) ▁blocked ▁the ▁Missouri ▁River , ▁which ▁at ▁that ▁time ▁flow ed ▁north ▁into ▁a ▁terminal ▁lake . ▁As ▁river water ▁and ▁gla cial ▁m elt water ▁po o led ▁at ▁the ▁base ▁of ▁the ▁gla cier , ▁it ▁created ▁Lake ▁Great ▁F alls . ▁All ▁but ▁ ▁of ▁Tower ▁Rock ▁was ▁covered ▁with ▁the ▁lake ' s ▁waters . ▁ ▁Native ▁Americans ▁were ▁well ▁acquaint ed ▁with ▁Tower ▁Rock . ▁The ▁B itter root ▁Sal ish ▁and ▁Lower ▁K oot en ay ▁often ▁passed ▁by ▁Tower ▁Rock ▁on ▁their ▁way ▁through ▁the ▁Adel ▁Mountains ▁Vol can ic ▁Field ▁to ▁hunting ▁grounds . ▁The ▁P ieg an ▁Black fe et ▁often ▁winter ed ▁near ▁present - day ▁Hel ena , ▁Mont ana , ▁and ▁passed ▁through ▁the ▁Adel ▁Mountains ▁Vol can ic ▁Field