HiRISE / MRO : ESP_018636_2745_RGB "North Polar Layers"
The North Polar layered deposits are a 3-kilometer thick stack of dusty water ice layers that are about 1000 kilometers across. The layers record information about climate stretching back a few million years into Martian history.
In many locations erosion has created scarps and troughs that expose this layering. The tan colored layers are the dusty water ice of the polar layered deposits; however a section of bluish layers are is visible below them. These bluish layers contain sand-sized rock fragments that likely formed a large polar dunefield before the overlying dusty ice was deposited.
The lack of a polar ice cap in this past epoch attests to the variability of the Martian climate, which undergoes larger changes over time than that of the Earth.