Original sentence: Ascraeus Mons and Pavonis Mons are at least 200 miles across and are over six miles above the plateau that they sit on--and, the plateau is three to four miles above the zero altitude of Mars.Studies have found that on Mars a fault may be as deep as 5 km, that is the break in the rock goes down to 5 km
Edited sentence: Ascraeus Mons and Pavonis Mons are at least 200 miles across and are over six miles above the plateau that they sit on—and, the plateau is three to four miles above the zero altitude of Mars.Studies have found that on Mars a fault may be as deep as 5 km, that is the break in the rock goes down to 5 km