ros ▁Vall es ▁in ▁the ▁Cop r ates ▁quad rangle . ▁ ▁L ay ers ▁in ▁Ice ▁Cap ▁ ▁Gul lies ▁Mart ian ▁g ul lies ▁are ▁small , ▁inc ised ▁networks ▁of ▁narrow ▁channels ▁and ▁their ▁associated ▁down s lo pe ▁sed iment ▁depos its , ▁found ▁on ▁the ▁planet ▁of ▁Mars . ▁They ▁are ▁named ▁for ▁their ▁res embl ance ▁to ▁terrest rial ▁g ul lies . ▁First ▁discovered ▁on ▁images ▁from ▁Mars ▁Global ▁Survey or , ▁they ▁occur ▁on ▁ste ep ▁s lop es , ▁especially ▁on ▁the ▁walls ▁of ▁cr aters . ▁Usually , ▁each ▁g ul ly ▁has ▁a ▁d end rit ic ▁alc ove ▁at ▁its ▁head , ▁a ▁fan - sh aped ▁apr on ▁at ▁its ▁base , ▁and ▁a ▁single ▁thread ▁of ▁inc ised ▁channel ▁linking ▁the ▁two , ▁giving ▁the ▁whole ▁g ul ly ▁an ▁hour glass ▁shape . ▁They ▁are ▁believed ▁to ▁be ▁relatively ▁young ▁because ▁they ▁have ▁few , ▁if ▁any ▁cr aters . ▁ ▁On ▁the ▁basis ▁of ▁their ▁form , ▁aspects , ▁positions , ▁and ▁location ▁amongst ▁and ▁apparent ▁interaction ▁with ▁features ▁thought ▁to ▁be ▁rich ▁in ▁water ▁ice , ▁many ▁research ers ▁believed ▁that ▁the ▁processes ▁car ving ▁the ▁g ul lies ▁involve ▁liquid ▁water . ▁However , ▁this ▁remains ▁a ▁topic ▁of ▁active ▁research . ▁ ▁, ▁ ▁| ▁ ▁Lat itude ▁dependent ▁mant le ▁ ▁Much ▁of ▁the ▁Mart ian ▁surface ▁is ▁covered ▁with ▁a ▁thick ▁ice - rich , ▁mant le ▁layer ▁that ▁has ▁fallen ▁from