▁by ▁following ▁the ▁Missouri ▁River . ▁W icki up ▁frames ▁were ▁often ▁built ▁in ▁the ▁area ▁and ▁re used ▁as ▁native ▁people ▁moved ▁to ▁their ▁summer ▁hunting ▁grounds ▁and ▁back ▁to ▁their ▁winter ▁cam ps . ▁The ▁P ieg an ▁Black fe et ▁considered ▁Tower ▁Rock ▁sacred , ▁and ▁conducted ▁cer emon ies ▁there . ▁Ind ividual ▁Black fe et ▁also ▁visited ▁the ▁site ▁alone ▁for ▁prayer ▁and ▁med itation . ▁ ▁Tower ▁Rock ▁received ▁its ▁modern ▁name ▁from ▁Mer iw ether ▁Lewis ▁on ▁July ▁ 1 6 , ▁ 1 8 0 5 . ▁Tower ▁Rock ▁marked ▁the ▁boundary ▁where ▁the ▁Lewis ▁and ▁Clark ▁Ex ped ition ▁left ▁the ▁Great ▁Pla ins ▁and ▁entered ▁the ▁Rock y ▁Mountains . ▁Having ▁completed ▁the ▁port age ▁around ▁the ▁Great ▁F alls ▁of ▁the ▁Missouri ▁and ▁made ▁enough ▁can o es ▁to ▁carry ▁their ▁b agg age , ▁the ▁expedition ▁set ▁out ▁from ▁White ▁Bear ▁Island ▁( a ▁little ▁more ▁than ▁ ▁south ▁of ▁present - day ▁Great ▁F alls , ▁Mont ana ) ▁on ▁July ▁ 1 5 . ▁Starting ▁near ▁dawn ▁on ▁July ▁ 1 6 , ▁Lewis ▁took ▁a iling ▁expedition ▁members ▁Jean ▁Bapt iste ▁Le page ▁and ▁John ▁Pot ts ▁and ▁set ▁out ▁on ▁foot ▁to ▁explore ▁ahead . ▁Following ▁an ▁Indian ▁trail , ▁they ▁passed ▁Half - Bre ed ▁Rap ids . ▁Lewis ▁and ▁his ▁compan ions ▁then ▁became ▁the ▁first ▁non - n atives ▁to ▁see ▁Tower ▁Rock ▁that ▁afternoon . ▁ ▁Lewis ▁gave ▁the ▁land mark ▁its ▁name