Valles Marineris: 4000 km long (about a fifth of the Martian circumference), up to 600 km wide and 7 km deep.
The Grand Canyon: 800 km long, up to 29 km wide and 1.6 km deep.
Highest and Lowest Points
The highest point is at the top of the volcano Olympus Mons and lies at an altitude of 27 km above the surface. The lowest point is at the bottom of the Hellas basin. It lies 4 km below the surface. The difference is nearly 31 km.
The difference between the highest and lowest points on Earth is only 20 km. Mount Everest is 8 848 meters high and the bottom of the Mariana Trench is 11 022 meters deep.
