Mars has mountains much like Earth. However, unlike many of the mountain ranges on Earth, Martian mountains were not created by plate techtonics. Olympus Mons, Ascraeus Mons, Arsia Mons, and Elysium Mons are all taller than Mount Everest. Pavonis Mons is slightly shorter, but has a much wider base.
All five of those mountains are shield volcanoes, which erupt but have low viscosity lava. The lava flows down the sides of the volcano, which lead to wide bases and low profiles. For the Martian volcanoes, lack of plate tectonics lead to all the shield volcanoes on Mars to get really wide and really tall.
Olympus Mons is the largest of these volcanoes. It is 21.4 km tall (from the peak to average surface elevation around its locality)and as shown in the picture below, the base has an area equivalent to the size of Arizona. This means that the slope of Olympus Mons is only 5 degrees from base to peak. Olympus Mons is not the tallest mountain in the solar system. That honor belongs to Rheasilvia on the asteroid Vesta. It has a height from base to peak of 22 km, though only 12 km are above the average surface elevation of Vesta. Mauna Kea and Mauna Loa are two shield volcanoes in the Hawaiian island chain. They have peaks only 4.2 km above sea level, but from base to peak they are 10.2 km.
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| Olympus Mons |
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| Tharsis Montes |
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| Elysium Mons
Mars is also home to one of the most extensive canyon systems in the solar system. Valles Mariners is a huge scar running across the landscape in the southern hemisphere. If we were able to place it on Earth, it would run from New York to Los Angeles. It is approximately 4000 km long send has a maximum depth of 7 km. Compare this to the Grand Canyon in Arizona, which is "only" 446 km long and 1.8 km deep. The Grand Canyon was shaped by the Colorado River, but it is unknown what formed the Valleys Marineris. It is believed that liquid water or volcanism formed it, but it could be a combination of both.
Valles Mariners
Lastly, Mars may have at one time liquid oceans. It does not anymore because of the atmospheric pressure (future post) and the low temperature. Images from Martian probes show evidence of ancient shorelines.
 
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