cias ▁and ▁ch urn ed ▁reg ol ith ▁forming ▁the ▁rough ▁terra ▁and ▁cr ater ▁depos its . ▁ ▁The ▁oldest ▁rocks ▁exposed ▁in ▁the ▁quad rangle ▁are ▁the ▁inter cr ater ▁pla ins ▁material ▁and ▁the ▁r ims ▁of ▁the ▁oldest ▁cr aters ▁and ▁bas ins . ▁Collect ively , ▁these ▁rocks ▁form ▁a ▁relatively ▁sub du ed ▁terrain ▁of ▁moder ate ▁relief . ▁They ▁are ▁similar ▁to ▁some ▁of ▁the ▁rolling ▁and ▁h illy ▁terra ▁and ▁h illy ▁and ▁p itted ▁materials ▁in ▁the ▁southern ▁lun ar ▁high lands , ▁particularly ▁in ▁the ▁Pur bach ▁( H olt , ▁ 1 9 7 4 ) ▁and ▁Ty cho ▁( P ohn , ▁ 1 9 7 2 ) ▁quadr angles . ▁The ▁inter cr ater ▁pla ins ▁unit ▁is ▁commonly ▁marked ▁by ▁the ▁soft ▁out lines ▁of ▁numerous ▁over la pping ▁secondary ▁cr aters ▁producing ▁a ▁sub du ed ▁hum mock y ▁texture . ▁It ▁is ▁grad ational ▁in ▁places ▁with ▁cr ater ed ▁pla ins ▁material , ▁which ▁forms ▁flat , ▁dens ely ▁cr ater ed ▁surfaces ▁similar ▁to ▁pre - Im b rian ▁pla ins ▁on ▁the ▁Moon ▁( Wil hel ms ▁and Mc C au ley , ▁ 1 9 7 1 ; ▁Scott , ▁ 1 9 7 2 ) ▁Although ▁both ▁the ▁cr ater ed ▁and ▁inter cr ater ▁pla ins ▁depos its ▁are ▁interpreted ▁to ▁be ▁vol can ic , ▁the ▁latter ▁has ▁been ▁highly ▁de grad ed ▁by ▁repeated ▁impact s ▁over ▁a ▁longer