The volcano is located in Mars's western hemisphere at approximately WikiMiniAtlas18°39′N 226°12′E / 18.65°N 226.2°E / 18.65; 226.2, just off the northwestern edge of the Tharsis bulge. The western portion of the volcano lies in the Amazonis quadrangle (MC-8) and the central and eastern portions in the adjoining Tharsis quadrangle (MC-9). Two impact craters on Olympus Mons have been assigned provisional names by the IAU. They are the 15.6 km (9.7 mi)-diameter Karzok crater ( WikiMiniAtlas18°25′N 131°55′W / 18.417°N 131.917°W / 18.417; -131.917) and the 10.4 km (6.5 mi)-diameter Pangboche crater ( WikiMiniAtlas17°10′N 133°35′W / 17.167°N 133.583°W / 17.167; -133.583). The craters are notable for being two of several suspected source areas for shergottites, the most abundant class of Martian meteorites.