Big Joe, the large rock just left of center is about 2 m (7 ft) wide. The top of the rock is covered with red soil. Those portions of the rock not covered are similar in color to basaltic rocks on Earth. This rock may be a fragment of a lava flow that was later ejected by an impact crater. The red color of the rocks and soil is due to an abundance of oxidized iron in the eroded material. In some areas of this scene rocky plains tend to dominate, while a short distance away drifts of regolith have formed.