This image shows a bright, rectangular-looking landform surrounded by a dark floor. How did this feature get here if it looks so different than its surroundings?
The feature resembles a plateau. Dark streaks mark steep slopes on its sides while the top appears flat. The slope streaks are not all the same age, as we see a variation in colors from faint to dark. Craters in a variety of sizes and ages pepper the entire rectangle, but the dark, textured floor has very few noticeable craters.
The evidence suggests that this rectangular feature is a high-standing “island” of older land surrounded by one or more younger lava flows. This landmass is located in Amazonis Planitia, a smooth plains area potentially formed by large-scale lava floods between the Tharsis and Elysium volcanic regions. As lava flowed into this area, the rectangular plateau was too high to cover completely, leaving a bright spot sticking out of the dark basalt floor for us to find. [More at link]