Smooth, dark volcanic basalt lines the bottom of the mare.

The Australe basin was formed in the Pre-Nectarian epoch, while the mare material inside formed in the Upper Imbrian epoch.

The basin was almost completely destroyed by impacts prior to the appearance of the mare.

[2] Unlike most of the lunar maria, Mare Australe has an uneven surface that is marked by a number of crater impacts.

The selenographic coordinates of this mare are 38.9° S, 93.0° E. The eastern half of the mare lies on the far side of the Moon, although it can be viewed in its entirety during periods of favorable libration.