Grimaldi 5.5°S, 68.3°W

Grimaldi, because of its size, must be counted as an impact basin (similar to Mare Humboltianum), whose lava-flooded central portion is bounded by an inner wall that is about 200 km in diameter. The outer wall, which is only partially remaining, has a diameter of over 400 km. Grimaldi may thus be classed as a multi-ring basin.

Running parallel to the southeastern portion of the inner crater wall are Rimae Grimaldi, with an overall length of 230 km (with a maximum width of 2 km). They are narrow linear rilles, probably produced by the tension forces when the lava flows contracted as they cooled. In the northern portion of the crater's floor there is a large volcanic dome with a summit crater. A few additional domes may be observed with larger telescopes under favourable lighting and seeing conditions. Grimaldi is associated with a mascon, a gravitational anomaly. Because Grimaldi is near the western limb of the Moon, observation of the Grimaldi Basin and its rille system requires favourable libration angles.

Riccioli 3.3°S, 74.6°W

Riccioli is a large complex crater, 145 km in diameter. The Rimae Riccioli lie in the southern portion of the crater's floor, and stretch for a total length of over 400 km. They are linear rilles with a maximum width of 1.5 km. The northern portion of the crater floor is lava-flooded.