Possible volcanic activity in the past? Olympus Mons is the largest (known) volcano in our solar system.
Right, I should also mention that it's cool that it's similar in composition.
edit on 31/10/2012 by CrikeyMagnet because: I sent too soon!
Scientists say the Martian soil at the rover Curiosity's landing site contains minerals similar to what's found on Hawaii's Mauna Kea volcano.An analysis revealed it contained feldspar and olivine, minerals typically associated with volcanic eruptions. Mission scientists say the Martian soil is similar to volcanic soil on the flanks of Mauna Kea.HuffPo