ition ing ▁the ▁state ▁of ▁Mont ana ▁to ▁build ▁a ▁state ▁highway ▁from ▁Cas cade ▁to ▁Wolf ▁Creek ▁through ▁the ▁Missouri ▁River . ▁This ▁project , ▁whose ▁route ▁was ▁on ▁the ▁west ▁bank ▁of ▁the ▁Missouri ▁and ▁largely ▁par alle led ▁the ▁rail road ▁tracks , ▁was ▁approved . ▁The ▁area ▁was ▁still ▁sp ars ely ▁settled , ▁and ▁little ▁bl ast ing ▁or ▁dig ging ▁had ▁to ▁be ▁done ▁as ▁the ▁route ▁went ▁around ▁Tower ▁Rock ▁to ▁the ▁west ▁rather ▁than ▁east . ▁Cont ract s ▁for ▁the ▁project ▁were ▁first ▁let ▁in ▁ 1 9 2 9 , ▁although ▁most ▁construction ▁occurred ▁in ▁ 1 9 3 0 ▁and ▁ 1 9 3 1 . ▁The ▁road ▁through ▁the ▁Missouri ▁River ▁can y on ▁was ▁completed ▁in ▁ 1 9 3 2 , ▁and ▁all ▁of ▁Highway ▁ 9 1 ▁in ▁Mont ana ▁opened ▁by ▁ 1 9 3 5 . ▁( The ▁Hard y ▁Bridge , ▁located ▁ ▁south ▁of ▁Tower ▁Rock , ▁was ▁constructed ▁as ▁part ▁of ▁this ▁project .) ▁The ▁segment ▁from ▁Cas cade ▁to ▁Wolf ▁Creek ▁provided ▁some ▁of ▁the ▁most ▁extensive ▁views ▁of ▁any ▁highway ▁in ▁the ▁state . ▁ ▁In ▁the ▁ 1 9 6 0 s , ▁Inter state ▁ 1 5 ▁( I - 1 5 ) ▁was ▁constructed ▁next ▁to ▁Tower ▁Rock . ▁The ▁general ▁route ▁of ▁I - 1 5 ▁was ▁established ▁by ▁ 1 9 5 7 ▁( a ▁year ▁after ▁passage ▁of ▁the ▁Federal ▁A id ▁Highway ▁Act ▁of