Ruby Falls is a series of underground cascading waterfalls totaling 145-foot (44 m) in Lookout Mountain, near Chattanooga, Tennessee, in the United States.
About 200 to 240 million years ago (in the Carboniferous Period, at the end of the Paleozoic Era), the eastern Tennessee area was covered with a shallow sea, the sediments of which eventually formed limestone rock. About 200 million years ago, this area was uplifted, forming Lookout Mountain and nearby ridges.
Slightly acidic groundwater running through cracks in the limestone slowly dissolved the relatively soluble rock, causing narrow cracks to widen into passages. This process, called chemical weathering, formed various caves to form inside Lookout Mountain.
Among them were Lookout Mountain Cave, which opened to the outside, and Ruby Falls Cave, which did not. The two were unconnected until developers joined them to create Lookout Mountain Caverns. Ruby Falls Cave is the upper of the two and contains a variety of geological formations and curiosities that Lookout Mountain Cave does not have.
Ruby Falls Cave features many of the more well-known types of cave formations (or speleothems) including stalactites and stalagmites, columns, drapery, and flowstone. The limestone in which the cave is formed is still relatively horizontal, just as it was deposited below sea level.
The Falls are located at the end of the main passage of Ruby Falls Cave, in a large vertical shaft. The stream, 1,120 feet underground, is fed both by rainwater and natural springs. It collects in a pool in the cave floor and then continues through the mountain until finally joining the Tennessee River at the base of Lookout Mountain.
According to en.wikipedia