Wikipedia
Crommlin Crater is an impact crater in the Oxia Palus quadrangle of Mars. It is located at 5.1° north and 10.2° west. It was named after Andrew C. Crommlin, a British astronomer (1865–1939). Parts of Crommlin crater display many thin layers. These may reflect different climates in the past—some of which were much wetter.
Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.
Many craters once contained lakes. Because some crater floors show deltas, we know that water had to be present for some time. Dozens of deltas have been spotted on Mars. Deltas form when sediment is washed in from a stream entering a quiet body of water. It takes a bit of time to form a delta, so the presence of a delta is exciting; it means water was there for a time, maybe for many years. Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet.
Wikicrommlin.jpg|Crommlin Crater with important parts labeled, as seen by CTX camera (on Mars Reconnaissance Orbiter). Wikicrommlinlayers.jpg|Layers in mound of Crommlin Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of previous image. Image:Crommlin Crater.JPG|Crommlin Crater Layered Deposit, as seen by HiRISE. The color blue in the photo is a false color. Image:Moundshigh.jpg|Crommlin Crater contains a layered mound that is higher than its rim. This drawing shows how it was formed when much of the material was eroded away.