Ladon Basin was a large impact structure that was filled in by the deposits from Ladon Valles, a major ancient river on Mars.
These wet sediments were altered into minerals such as various clay minerals. Clays imply chemistry that may have been favorable for life on ancient Mars, if anything lived there, so this could be a good spot for future exploration by rovers and perhaps return of samples to Earth.
Image cutout is less than 5 km (3 mi) across and the spacecraft altitude was 260 km (162 mi). For the full image including scale bars, visit the source link.