way ▁reached ▁White ▁Bear ▁Island ▁on ▁July ▁ 1 9 . ▁ ▁Rail road , ▁settlement , ▁and ▁high ways ▁The ▁Missouri ▁River ▁can y on ▁between ▁Hel ena ▁and ▁Cas cade ▁was ▁largely ▁by pass ed ▁by ▁white ▁sett lers ▁for ▁the ▁next ▁ 6 5 ▁years . ▁In ▁part , ▁this ▁was ▁because ▁easier ▁routes ▁allowed ▁access ▁to ▁the ▁western ▁mountains ▁and ▁valle ys , ▁but ▁also ▁because ▁the ▁P ieg an ▁Black fe et ▁continued ▁to ▁claim ▁the ▁area ▁as ▁their ▁own ▁and ▁were ▁not or iously ▁host ile ▁to ▁intr ud ers . ▁ ▁From ▁ 1 8 5 9 ▁to ▁ 1 8 6 0 , ▁the ▁M ull an ▁Road ▁was ▁constructed ▁from ▁Fort ▁Bent on , ▁then ▁part ▁of ▁Dak ota ▁Territ ory , ▁to ▁Fort ▁Wal la ▁Wal la , ▁Washington ▁Territ ory . ▁The ▁M ull an ▁Road ▁by pass ed ▁Tower ▁Rock ▁and ▁its ▁can y on : ▁The ▁M ull an ▁Road ▁only ▁followed ▁the ▁Missouri ▁River ▁until ▁it ▁reached ▁the ▁D ear born ▁River . ▁R ather ▁than ▁enter ▁the ▁Missouri ▁River ▁can y on , ▁it ▁struck ▁in land ▁and ▁passed ▁south ▁through ▁a ▁wide , ▁flat ▁pra irie ▁about ▁ ▁west ▁of ▁the ▁river . ▁This ▁allowed ▁the ▁road ▁to ▁sk irt ▁the ▁rug ged ▁Adel ▁Mountains ▁Vol can ic ▁Field . ▁The ▁M ull an ▁Road ▁then ▁followed ▁the ▁valley ▁of ▁Little ▁Pr ick ly ▁Pear ▁Creek ▁back ▁to ▁the ▁Missouri ▁River ▁near ▁present - day ▁Wolf ▁Creek