Oxia Planum is an ancient (Noachian epoch) terrain situated to the east of Chryse Planitia at about 18 degrees north. The OMEGA infrared spectrometer on board Mars Express, and CRISM onboard the Mars Reconnaissance Orbiter, have identified iron-magnesium rich clays like smectite over hundreds of square kilometers.
This image uses HiRISE to show what the surface looks like and whether it is feasible to land a rover on it. In this instance the image was taken with the ExoMars rover in mind (Oxia Planum is one of the leading candidate sites for that mission)… [More at link]