▁Minnesota ▁and ▁south western ▁Wisconsin ▁are ▁in ▁the ▁Dr ift less ▁Area , ▁which ▁was ▁not ▁covered ▁by ▁the ▁last ▁gla ci ation , ▁and ▁therefore ▁is ▁not ▁covered ▁by ▁deep ▁layers ▁of ▁gla cial ▁till . ▁ ▁The ▁so ils ▁therefore ▁are ▁thin ▁and ▁less ▁able ▁to ▁retain ▁water ; ▁they ▁lie ▁at op ▁por ous ▁rock ▁into ▁and ▁through ▁which ▁surface ▁waters ▁can ▁rapidly ▁d rain ▁into ▁the ▁water ▁table . ▁ ▁The ▁highly ▁disse cted ▁top ography , ▁character ized ▁by ▁ste ep ▁hills ▁and ▁bl uff s ▁and ▁deep ▁cou le es , ▁gives ▁ste ep ▁grad ients ▁to ▁the ▁d rain age ▁and ▁makes ▁streams ▁highly ▁er os ive . ▁ ▁As ▁the ▁ra ins ▁far ▁exceed ed ▁the ▁absor ption ▁rate ▁ ▁of ▁ 1 . 5   in ches ▁( 3 . 8   cm ) ▁in ▁six ▁hours , ▁flash ▁flo ods ▁rapidly ▁overflow ed ▁the ▁water ▁courses ▁and ▁spread ▁across ▁the ▁valley ▁flo ors . ▁ ▁The ▁towns ▁of ▁Stock ton , ▁Houston , ▁El ba , ▁Minnesota ▁City , ▁and ▁port ions ▁of ▁Win ona , ▁on ▁the ▁Mississippi ▁River , ▁were ▁ev acu ated . ▁Cit iz ens ▁were ▁moved ▁to ▁Saint ▁Mary ' s ▁University ▁in ▁Win ona , ▁Lew ist on , ▁and ▁C aled onia , ▁Minnesota . ▁Mass ive ▁bl uff s ▁gave ▁way ▁in ▁Brow ns ville ▁and ▁several ▁homes ▁were ▁completely ▁was hed ▁away . ▁Governor ▁Tim ▁P aw l enty ▁ordered ▁ 2 4 0