In this photograph, the great canyon called 'Mariner Valley' is clear.
There are a number of round features, which are volcanoes.
One of the Martian volcanoes, Olympus Mons, is the biggest volcano in the solar system.
Olympus Mons is a shield volcano.
It is 624 km (374 miles) in diameter.
That's about the same size as France, or the state of Arizona
Olympus Mons is 25 km (16 miles) high
Its base is encircled by a 6 km (4 miles) high cliff.
A crater 80 km (50 miles) wide is located at the summit of Olympus Mons.
In comparison, the largest volcano on Earth is Mauna Loa on Hawaii.
Mauna Loa is a shield volcano 10 km (6.3 miles) high and 120 km (75 miles) across.
The volume of Olympus Mons is about 100 times larger than that of Mauna Loa.