This is a closeup image of the heavily cratered area just east of the Sea Of Clouds (Mare Nubium) on the moon, taken when the moon was about 70% illuminated, with the terminator splitting the Mare Nubium.

The Mare Nubium is labeled in blue, and craters are labeled in red. West of the craters Thebit and Arzachel is the Rupes Recta, labeled in yellow. The Rupes Recta is an escarpment along a fault line and is about 68 miles long. When the solar angle is shallow, as when it is near the terminator, the Rupes Recta casts a shadow that makes it appear from Earth to be a steep cliff, but it actually has a relatively shallow grade, rising about 900 feet in its 1.5 mile width.