Geological Chronicle
Vallis Snellius is a linear valley situated in the rugged southeastern part of the visible lunar surface, south of the Mare Fecunditatis. Reaching a maximum length of 592 km, with an official diameter of 640 km, it is the longest named valley on the Moon. The feature is radial to the Mare Nectaris basin to the west-northwest, much like Vallis Rheita to the southwest, and the two likely share a common origin.
Although linear, the valley is irregular in shape and has been heavily worn by impact erosion, making it difficult to trace across the surface. Near the northern part of the valley lies the crater Borda, and the valley cuts through the southern half of the floor of crater Snellius, the landmark from which it is named.