Water ice mixed with dust form the residual north polar ice cap (brown color). Seasonal frost of relatively pure ice (white color) partly blankets the polar deposits. A large trough, which is occupied by linear sand dunes (dark band), exposes polar layered deposits. The layered deposits hold a partial record of the history of atmospheric activity and climate of Mars. Center of picture is at latitude 82 degrees N., longitude 84 degrees W. Viking Orbiter Picture Numbers 82B11-12 (violet), 82B15-16 (green), and 82B17-18 (red) at 53 m/pixel resolution. Picture width is 106 km. North is 6 degrees counter-clockwise from top.