Valley on the Moon is a term used to describe a type of feature found on the surface of the moon. It is a long, narrow depression that is usually formed by the collapse of the surface due to erosion or tectonic activity. The two crossword solutions for this term are RILL (4 letters) and RILLE (5 letters). RILL is a small stream or channel that is usually dry and has steep sides. RILLE is a larger version of a RILL, with deeper and wider channels. Both of these features can be found on the moon's surface.