Today's Image of Mars comes from the High Resolution Stereo Camera (HRSC) aboard the Mars Express Orbiter and shows the Eumenides Dorsum mountains, which cover an area of 12,000 square kilometers. The mountains are to the west of the Tharsis Quadrangle and form part of the Medusa Fossae region, which scientists believe is covered by a blanket of volcanic ash.
The region is full of features carved into layers of sedimentary rock by wind erosion. The smooth area in the center of this image is a result of that terrain being more resistant to erosion than the surrounding area. This indicates that the surface of that area is made up of volcanic rock, as opposed to more easily eroded sedimentary rock.
Clicking on this image will take you to the original high resolution image from Mars Express. [See their article on the Eumenides Dorsum mountains]