Two kilometers above the lava flows of Mars' Tharsis Bulge region, a geologist collects samples from the eastern cliff at the base of Olympus Mons, the solar system's largest known shield volcano. To better understand the evolution of the Arizona-sized volcano, the scientist investigates the layers of hardened lava that make up the massive feature. The block-like nature of the rock face, caused by columnar jointing, is similar to features on Earth, such as the Devil's Tower in Wyoming