▁d rain age ▁bas in ▁has ▁been ▁proposed ▁as ▁a ▁source ▁of ▁the ▁cat ast roph ic ▁flo od w aters ▁that ▁are ▁hypoth es ized ▁to ▁have ▁formed ▁the ▁circum - Ch ry se ▁out flow ▁channels , ▁and ▁the ▁north western ▁slope ▁valle ys ▁( NS V s ) ▁to ▁the ▁north west ▁of ▁the ▁Th ars is ▁R ise . ▁ ▁A ▁number ▁of ▁highly ▁disse cted ▁features ▁with ▁sum mit ▁de press ions ▁are ▁present ▁as ▁isolated ▁mountains ▁across ▁the ▁Cop r ates ▁R ise , ▁the ▁Th aum asia ▁high lands , ▁Da ed alia ▁Plan um , ▁and ▁Terra ▁Sir enum ▁and ▁are ▁thought ▁to ▁be ▁the ▁ancient ▁edific es ▁of ▁high land ▁vol can ic ▁activity . ▁Despite ▁their ▁location ▁and ▁morph ology , ▁they ▁have ▁been ▁strat ig raph ically ▁found ▁to ▁cross - cut ▁younger ▁terra ins ▁( r anging ▁from ▁No ach ian ▁to ▁early ▁H esper ian ▁age ) ▁and ▁thus ▁are ▁probably ▁not ▁the ▁rem nant ▁mass ifs ▁of ▁a ▁put ative ▁Th ars is ▁impact ▁bas in . ▁These ▁put ative ▁ancient ▁vol cano es ▁are ▁morph olog ically ▁distinct ▁from ▁the ▁H esper ian ▁period ▁Th ars is ▁shield ▁vol cano es ; ▁they ▁have ▁been ▁hypoth es ized ▁to ▁be ▁composed ▁of ▁inter bed ded ▁layers ▁of ▁la va ▁and ▁py ro cl astic ▁rock ▁compar able ▁to ▁terrest rial ▁strat ov ol cano es . ▁If ▁this ▁anal ogy ▁holds , ▁it ▁is ▁possible ▁that ▁these ▁explos