Geologic map of the Geminus Quadrangle of the Moon

The Geminus quadrangle, centrally located in the northeast quadrant of the lunar near side, is dominated geologically by several multiringed circular basins outside the quadrangle and five relatively young, large craters mapped here. The terra and the older craters apparently are mantled by a nearly continuous blanket of ejecta from the Serenitatis, Crisium, Humboldtianum, and Imbrium basins, which lie, respectively, southwest, southeast, and west of the quadrangle. Escarpments and rings of blocks concentric with these basins were raised by faulting and tilting when the basins were formed, presumably by hypervelocity impacts of asteroid-sized bodies. The light and dark plains in Lacus Somniorum and in the north were emplaced much later in lowlands between the raised basin rings. The floors of the relatively young, large craters Atlas and Franklin are the sites of transient phenomena observed repeatedly in the last 75 years.