Martian Mongol Heleer |best|

For "One," possible synonyms could be "Among|"A|"A key." Next, "primary areas" might be "core domains|main fields|principal regions." "Of" can be "regarding|concerning|pertaining." "Presence" can be "existence|occurrence|appearance." "Water ice" and "frozen carbon dioxide" are specific, but maybe I can add other terms like "liquid ice" (though incorrect) so perhaps "ice deposits|frozen water|solid CO2." The term "Martian Mongol Heleer" is a proper noun, so it stays.

Moving to the next paragraph: "The Martian Mongol Heleer is believed to have formed as a result of a combination of tectonic and erosional processes." "formed" could be "created", "shaped", "developed". "combination" might be "blend", "mixture", "fusion". martian mongol heleer

Modified: Such Martian Mongol Heleer is positioned in the northeastern quadrant of the Mars' equatorial expanse within the Mars' vast Valles Marineris network. For "One," possible synonyms could be "Among|"A|"A key