We see here a terrain with an incredible morphologic dichotomy: a relatively smooth region that transitions into sharp ridges . These ridges, aligned in the nearly same direction, are called yardangs. Yardangs are not unique to Mars. Many yardangs can be found on Earth, in very dry regions with strong prevailing winds.

Yardangs are formed when a surface that is composed of materials of differing strengths (i.e., of both harder and softer materials) is shaped by the abrasive action of sand and dust carried by the wind. In this case, and given the proximity of the Apollonaris Patera volcanic center, we think that these wind-carved deposits are comprised of volcanic ash and pyroclastics that erupted from Apollonaris when it was last active in the not-too-distant geologic past.

Over time, the softer materials (likely volcanic ash) were eroded away, leaving behind the harder materials in the form of elongated ridges that are parallel to the direction of the prevailing wind. The end result is a stunning, out-of-this-world display of yardangs, sculpted with the artistic chisel of the Martian wind.
Written by: Elizabeth Silber, Livio Tornabene, and Kayle Hansen   (12 August 2015)

More info and image formats at http://hirise.lpl.arizona.edu/ESP_041929_1675

Image: NASA/JPL/University of Arizona