This field of sand dunes occurs within Chasma Borealis.

The dark sand dunes in this image are only a very small portion of the sand sea that surrounds the north polar cap of Mars.

The dark sand dunes in this image are only a very small portion of the sand sea that surrounds the north polar cap of Mars.

The dark sand dunes in this image are only a very small portion of the sand sea that surrounds the north polar cap of Mars.

This extensive dune field in located on the floor of Rabe Crater in Noachis Terra.

This extensive dune field in located on the floor of Rabe Crater in Noachis Terra.

This extensive dune field in located on the floor of Rabe Crater in Noachis Terra.

The depressions in the rim of this unnamed crater in Terra Sabaea are being filled with new material. The surface texture of the new material is different from the surrounding older material.

The depressions in the rim of this unnamed crater in Terra Sabaea are being filled with new material. The surface texture of the new material is different from the surrounding older material.

The depressions in the rim of this unnamed crater in Terra Sabaea are being filled with new material. The surface texture of the new material is different from the surrounding older material.

Many craters in the northern plains look like the one in this image - interior filled almost to the rim, narrow and steep ejecta surrounding the rim, little or no remaining distant ejecta. It is assumed that the climate in the region has affected the appearance of these craters.

Many craters in the northern plains look like the one in this image - interior filled almost to the rim, narrow and steep ejecta surrounding the rim, little or no remaining distant ejecta. It is assumed that the climate in the region has affected the appearance of these craters.

Many craters in the northern plains look like the one in this image - interior filled almost to the rim, narrow and steep ejecta surrounding the rim, little or no remaining distant ejecta. It is assumed that the climate in the region has affected the appearance of these craters.

This image shows part of the large dune field (or erg) that exists surrounding the north polar ice cap.

This image shows part of the large dune field (or erg) that exists surrounding the north polar ice cap.