Today's Image of Mars is of crescent shaped depressions on the surface created by strong winds. The Earth equivalent are called blowouts, but occurrences on Mars are much larger than those on Earth. This image is from North Azimuth on Mars, but there are many similar features in other parts of Mars.
On Mars, wind is the currently the primary cause of erosion. [How strong are the winds on Mars?] There is evidence that water helped shape much of the Martian surface, but over billions of years Mars is now devoid of the massive seas, rivers, and lakes that once played a part in shaping the planet.
This image links to the original image page from Mars Odyssey's THEMIS.