▁With ▁the ▁North ▁American ▁Pl ate ▁overrid ing ▁the ▁Pacific ▁Pl ate , ▁episodes ▁of ▁vol can ic ▁ igne ous ▁activity ▁pers isted . ▁Rem n ants ▁of ▁the ▁Hann eg an ▁Cal der a ▁can ▁be ▁seen ▁on ▁the ▁er oded ▁sout heast ▁face ▁of ▁Hann eg an ▁Pe ak . ▁The ▁cal der a ▁er upt ed ▁four ▁million ▁years ▁ago ▁during ▁the ▁P li oc ene ▁epo ch , ▁and ▁was ▁a ▁prec ursor ▁to ▁the ▁vol can ism ▁of ▁M t . ▁Baker . ▁In ▁addition , ▁small ▁fragments ▁of ▁the ▁ocean ic ▁and ▁contin ental ▁l ith os phere ▁called ▁ter ran es ▁created ▁the ▁North ▁C asc ades ▁about ▁ 5 0 ▁million ▁years ▁ago . ▁ ▁During ▁the ▁Ple ist oc ene ▁period ▁d ating ▁back ▁over ▁two ▁million ▁years ▁ago , ▁gla ci ation ▁adv ancing ▁and ▁retre ating ▁repeatedly ▁sc oured ▁the ▁landscape ▁leaving ▁depos its ▁of ▁rock ▁de br is . ▁The ▁U - sh aped ▁cross ▁section ▁of ▁the ▁river ▁valle ys ▁are ▁a ▁result ▁of ▁recent ▁gla ci ation . ▁U pl ift ▁and ▁fault ing ▁in ▁combination ▁with ▁gla ci ation ▁have ▁been ▁the ▁dominant ▁processes ▁which ▁have ▁created ▁the ▁tall ▁pe aks ▁and ▁deep ▁valle ys ▁of ▁the ▁North ▁C asc ades ▁area . ▁ ▁See ▁also ▁▁ ▁Ge ology ▁of ▁the ▁Pacific ▁North west ▁ ▁Geography ▁of ▁the ▁North ▁C asc ades ▁ ▁References ▁ ▁External ▁links ▁ ▁Hann eg an ▁Pe ak : ▁Mountain ▁Fore cast