This HiRISE image shows a group of cones, shield-like features, and round mounds. They are a few hundred meters to kilometers in diameter. Possible origins include sedimentary (mud) volcanism and magmatic volcanism. HiRISE data are essential for evaluating these hypotheses.
Photo credit: NASA/JPL/University of Arizona
Note: This image is located in southern Chryse Planitia, north of the "mouth" of Simud Valles, and about halfway between the landing sites of Viking 1 and Pathfinder.