Rima Ariadaeus

Ariadaeus is the reference example of a lunar graben: a strip of crust dropped between two parallel normal faults, with no volcanic deposits detected along it. It runs 247 km across both mare and highland terrain and takes no notice of either, neither following the slope nor breaking at the boundary. That rules out a collapsed lava tube or a flow channel and leaves crustal extension as the mechanism.

Where it crosses older wrinkle ridges, the ridges are offset by the trough rather than the reverse, dating the faulting as the younger event. Apollo 10 photographed the rille obliquely from low orbit in 1969.