This image shows a portion of the floor in Palos Crater. The floor appears bumpy with high-standing layered knobs. Most of the terrain on the floor is weathering into meter-size polygonal blocks. The circular structures in the image, many of which are filled with darker aeolian material, are eroded impact craters.
Palos Crater is breached in the south by the 180 kilometers-long Tinto Vallis. Water transported along Tinto Vallis could have could have collected into Palos Crater to form a lake that later drained to the north. Sediments carried by Tinto Vallis would have also been deposited within Palos Crater so the layered unit we see along the floor today could represent these fluvial sediments.
Photo credit: NASA/JPL/University of Arizona
Note: Palos Crater and Tinto Vallis are located in the Mare Tyrrhenum Quadrangle of Mars. This area lies southeast of Isidis Planitia.