A comprehensive study of the Elysium region has revealed evidence of widespread ground-ice, whose concentration and depth has varied considerably. Ejecta mobility and crater morphology analyses of a database of 7289 craters (which range in diameter from 1.875 to over 160 km) have been used to investigate the distribution of ice between longitudes 245¿--155¿ and latitudes 20¿S--45¿N, an area incorporating all of the Elysium Quadrangle and large portions of Amenthes, Amazonis, Mare Tyrrhenum, Aeolis, Memnonia, Cebrenia, and Diacria Quadrangles. Assuming that the observed variations in the crater characteristics are the result of the incorporation of varying concentrations of subsurface volatiles, the ice distribution is shown to be strongly dependent upon latitude, though its concentration varies with depth and is strongly influenced by geological setting. Important differences have been detected in the distribution of southern and northern lowland ground-ice. While there is substantial evidence of near-surface ice in the northern lowlands, where near-surface limits are strongly influenced by latitude, the greatest concentrations of subsurface ice occur at much greater depths in the southern highlands. In addition, the ice appears to be enriched at depth in the Elysium Lavas, and nearer to the surface in deposits located to the northwest of Elysium Mons and in the Vastitas Borealis Formation. This distribution suggests that several ice-emplacement mechanisms have operated on Mars, including the enrichment of the deeper ice by juvenile water from beneath the Elysium volcanic province, and the redistribution to the lowlands of a highly concentrated ice reservoir from a great depth within the highlands. ¿ American Geophysical Union 1993