Streamlined Island in Kasei Valles (Saturated Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga - Lunexit Team)

In this picture there is a Streamlined Island: one of many observed in the large outflow channels on Mars. This outflow channel is called Kasei Valles, and is one of the largest catastrophic outflow channels on Mars.
The Streamlined Island forms as water flows through the channel, but is blocked by some sort of obstacle, such as a crater or other topographic landform. In this HiRISE image, we only see the very tail end of the Streamlined Island, which is over 118 Km in length.
The platy surface within the channels has been attributed to either later lava or mud flows along the surface. The island itself is quite dusty and covered in small craters, so the island may be quite old. Along the edge of the island, however, you can see individual layers of rock.
These layers represent individual rock units that may be volcanic or sedimentary in origin.