Geologic map of the Iapygia Quadrangle of Mars

The Iapygia quadrangle, in the equatorial region of Mars just north of the Hellas basin, is mainly ancient, hilly, and cratered upland terrain. The southern one-third of the quadrangle is dominated by mountain and knobby materials representing mountains of pre-Hellas material and material related to the Hellas basin and mappable in a 500-km-wide zone circumjacent to it. The northeast quadrant of the quadrangle contains two large arcuate structural scarps and moderately low-albedo mountain material and knobby deposits, both associated with formation of the Isidis basin (Meyer and Grolier, 1977). The major part of the Iapygia quadrangle is mapped as hilly and cratered upland materials units with subordinate various plains deposits. Although the southern rim of the Syrtis Major basin coincides with the northern margin of the quadrangle along the equator from 285 degrees to 295 degrees W., no structural features or ejecta associated with this basin have been identified in either the Iapygia or Sytris Major (MC-13) quadrangles. A dominant feature of the landscape within Iapygia is the 475-km-diameter basin-crater Huygens, which shows subtle evidence of having an inner ring structure (Wilhelms, 1973). A second basin-sized crater, Schroeter (265-km-diameter), shares its northern rim with the Syrtis Major quadrangle (MC-13) and has a more distinct inner ring structure than Huygens.