▁were ▁formed ▁during ▁the ▁w an ing ▁stages ▁of ▁high - imp act ▁flux ▁when ▁the ▁surface ▁was ▁virt ually ▁s atur ated ▁with ▁cr aters ▁and ▁bas ins . ▁Later ▁cr ater ing ▁history ▁records ▁a ▁decre asing ▁impact ▁flux : ▁of ▁cr aters ▁larger ▁than ▁ 5 0   km ▁diameter , ▁ 4 2 ▁are ▁class ed ▁as ▁c 3 ; ▁ 1 9 ▁cr aters ▁are ▁assigned ▁to ▁c 4 ; ▁and ▁ 9 ▁cr aters ▁are ▁c 5 . ▁There ▁is ▁also ▁a ▁decrease ▁in ▁the ▁size ▁of ▁the ▁largest ▁cr ater ▁or ▁bas in ▁formed ▁in ▁each ▁age ▁class ▁from ▁c 2 ▁to ▁c 5 . ▁ ▁Str ucture ▁▁ ▁Struct ural ▁features ▁are ▁sparse ▁or ▁un resol ved ▁in ▁this ▁part ▁of ▁Mercur y . ▁The ▁K ui per ▁quad rangle ▁apparently ▁has ▁none ▁of ▁the ▁scar ps ▁that ▁occur ▁elsewhere ▁on ▁the ▁planet ▁that ▁have ▁been ▁interpreted ▁as ▁high - angle ▁reverse ▁fault s . ▁The ▁most ▁prominent ▁structures ▁are ▁the ▁rings ▁associated ▁with ▁some ▁large ▁cr aters ▁or ▁bas ins , ▁fault s ▁that ▁tran sect ▁cr ater ▁flo ors , ▁and ▁lo b ate ▁scar ps ▁and ▁rid ges ▁in ▁the ▁pla ins ▁materials . ▁Most ▁of ▁the ▁fault s ▁and ▁scar ps ▁that ▁tran sect ▁cr ater ▁flo ors ▁clearly ▁del ine ate ▁cr ater - fill ing ▁materials ▁standing ▁at ▁different ▁levels , ▁and ▁in ▁at ▁least ▁two ▁cr aters ▁( 1 9 ° ▁S ., ▁ 3 1 ° ;