▁Saint - Louis " ▁( s outh ▁shore ), ▁as ▁well ▁as ▁by ▁rail . ▁Up stream , ▁this ▁valley ▁is ▁served ▁by ▁the ▁Cons ol ▁P aper ▁road ▁and ▁a ▁few ▁other ▁secondary ▁forest ▁roads ▁for ▁forest ry ▁and ▁recre ational ▁tour ism ▁activities . ▁ ▁Forest ry ▁is ▁the ▁main ▁economic ▁activity ▁in ▁this ▁valley ; ▁industrial ▁and ▁port ▁activities , ▁second ; ▁recre ational ▁tour ism ▁activities , ▁third . ▁ ▁The ▁surface ▁of ▁the ▁Mars ▁river ▁is ▁usually ▁fro zen ▁from ▁the ▁beginning ▁of ▁December ▁to ▁the ▁end ▁of ▁March , ▁however ▁the ▁safe ▁circul ation ▁on ▁the ▁ice ▁is ▁generally ▁done ▁from ▁mid - Dec ember ▁to ▁mid - M arch . ▁ ▁Geography ▁ ▁T aking ▁its ▁source ▁at ▁the ▁mouth ▁of ▁a ▁small ▁lake ▁at ▁ ▁above ▁sea ▁level ▁in ▁the ▁Laurent ides ▁Wild life ▁Reserve , ▁the ▁" riv ière ▁à ▁Mars " ▁flows ▁from ▁south ▁to ▁n ortheast ▁in ▁a ▁descent ▁compr ising ▁several ▁tum ult uous ▁and ▁rug ged ▁segments . ▁The ▁" riv ière ▁à ▁Mars " ▁flows ▁over ▁ ▁with ▁a ▁drop ▁of ▁ ▁especially ▁in ▁the ▁forest ▁zone ▁except ▁the ▁last ▁segment ▁of ▁ ▁in ▁industrial ▁zone ▁and ▁urban ▁at ▁the ▁end ▁of ▁the ▁course , ▁according ▁to ▁the ▁following ▁segments : ▁ ▁Upper ▁course ▁of ▁the ▁rivière ▁à ▁Mars ▁( segment ▁of ▁) ▁▁▁ ▁to ▁the ▁north ▁in ▁a ▁deep ▁valley ▁crossing ▁Lac ▁Tur c otte ▁( length : ▁; ▁alt itude : ▁) ▁at ▁its ▁peak ▁length ,