On the Beauty of Yardangs

Some geological materials (like solid rock) are incredibly tough, but others (like piles of volcanic ash) are quite soft. Some materials are soft enough that they can be eroded by the wind alone and yield landscapes that look like what we see in this HiRISE image. The long straight ridges seen here are called yardangs and they form on Mars (and Earth) when the wind strips away the inter-ridge material. This process is greatly aided when the wind is also blowing sand along.