The Viking Lander 2 site in Utopia Planitia has more and larger blocks of stone than does the Viking Lander 1 site in Chryse Planitia. The stones are probably ejecta from impact craters near the Lander 2 site. Many of the rocks are angular and are thought to be only slightly altered by the action of wind and other forms of erosion. Drifts of sand and dust are smaller and less noticeable at the Lander 2 site. The overall red coloring of the Martian terrain is due to the presence of oxidized iron in the regolith. The pink color of the sky is caused by extremely fine red dust that is suspended in Mars' thin atmosphere.