Geologic map of the Grimaldi quadrangle of the Moon

The Grimaldi quadrangle lies at the southwest margin of Oceanus Procellarum about 1,000 km east of Orientale, the youngest of the lunar multi-ringed basins. The distal ends of the ejecta blanket surrounding the Orientale basin partly covers the western third of the quadrangle. The relatively small, two-ring Grimaldi basin is in the northwest corner of the quadrangle, and the Humorum basin lies about 750 km to the southeast. A vestigial multi-ring basin mostly engulfed by mare appears to control the distribution of terra and mare along the southwest margin of Oceanus Procellarum; the craters Hansteen and Billy are on a northwest-trending topographic high which represents part of the ring system of this basin. Terra materials of distinctive texture, apparently unrelated to multi-ring basins and probably of volcanic origin, occupy the central parts of the quadrangle.