Today's Image of Mars is of the floor of the trough Tithonium Chasma, located in Valles Marineris, a large canyon system on Mars. As discussed in yesterday's Mars Photo of the Day, scientists are interested in these canyon systems because they provide a view of older material beneath the surface, which can provide insight into the past climate of Mars and changes that occurred.
Mars Reconnaissance Orbiter's CRISM has determined that sulfates and iron oxides are present in the general region in the form of layered deposits. This implies the past existence of water because sulfates are typically formed in the presence of water.
This photo links to the original captioned photo by HiRISE.