The proposed investigation will provide new constraints on the geologic evolution of the Martian surface by compiling and analyzing crater size-frequency distributions for crater ejecta and crater floor deposits in southern Tharsis (Arsia Mons, Daedalia Planum, and Syria Planum), Hesperia Planum, and Deuteronilus Mensae. The impact craters selected for analysis will provide specific lower and upper age constraints on Martian geologic activity on the basis of observed superposition or embayment relationships. This study will integrate the proposal team¿s experience in geologic mapping and stratigraphic studies of Mars, Martian surface processes, and Martian chronology and will utilize new high-resolution datasets (e.g., Mars Reconnaissance Orbiter Context Camera, Mars Express High Resolution Stereo Camera, and Mars Odyssey Thermal Emission Imaging System) that now allow the ages of individual craters to be determined and utilized as local stratigraphic markers.