Geological Chronicle
Mairan occupies a highland peninsula situated between Oceanus Procellarum to the west and Mare Imbrium to the east. Dated to the Late Imbrian epoch, the crater spans 39.49 kilometers across and retains a sharp outer rim that has avoided significant erosion or subsequent impact disruption. Its inner walls display terracing that steps down to a relatively flat interior floor, framed by rough, irregular terrain peppered with tiny craters to the south and west.
Due west across the mare lies a volcanic complex known as the Mairan Hills or Mairan Domes, comprising the summit depression Mairan T alongside three satellite domes. These steep, bright features formed across two eruptive episodes dated to 3.75±0.1 and 3.35±0.2 billion years ago, extruding viscous silicic lava concurrently with regional mare basalt flows. The southernmost dome consists of nearly pure quartz with thorium concentrations reaching 83±19 ppm.
Along the southwest margin of the highland peninsula, the sinuous rille Rima Mairan traces a north–south course for roughly 100 kilometers. Most of the neighboring volcanic complex, save for the highest dome summits, now lies buried beneath the surrounding mare surface.