Photographic evidence from NASA's Lunar Reconnaissance Orbiter (LRO) show signs of stretching and contracting of the lunar surface. These suprising findings demonstrate that the moon is not a as geologically static as once thought. The moon isn't just a solid chunk of rock orbiting around the Earth.
Tom Watters from the Smithsonian Institution's National Air and Space Centre for Earth and Planetary Studies notes "The moon is actually expanding or stretching and being pulled apart in some small areas and by a little bit."
Parallel faults are caused by this stretching, forming valleys or "graben" visible to the LRO.
In indepth discussion of this lunar evolution can be found at NASA's LRO website.