Seen here is the largest valley on the Moon, Vallis Schröteri. Comparable to the Grand Canyon on Earth, Vallis Schröteri is approximately 160 kilometers long, up to 11 kilometers wide and almost 0.5 kilometers deep.
The Moon is home to a lot of lava channels, which formed at times when it was volcanically active. Narrow and deep channels/valleys known as rilles are found at multiple places on the Moon. Such rilles are thought to have formed when large volumes of magma erupted from volcanic vents and flowed rapidly on the surface.
The rille of Vallis Schröteri seems to have its source vent at the “Cobra Head” like feature seen to the middle-right in the image. The sinuous nature (river-like shape) of the rille however, is a mystery. Look closely and you will see that there is another (secondary) rille within the primary rille! As seen to the left in the image, the secondary rille extends far beyond the primary one. Such nested form of valleys indicate a possibility of multiple eruptive events having occurred in the past.
Here’s an annotated and rather-gorgeous oblique view of the rille to get a complete idea.