The Ruby Falls Cave is located deep in the heart of Lookout Mountain. It is a limestone cave (sometimes called a Solution Cave).
At one time, the water table was much higher and the Ruby Falls Cave was at the top of it. Rushing water flowed through it for many years washing out the cave and enlarging the faults and cracks. The water table has since lowered and that explains the lack of water in the cave.
The Falls are located at the end of the main passage of Ruby Falls Cave, in a large vertical shaft. The stream, 1120 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. While Ruby Falls Cave combines with Lookout Mountain Cave to form the Lookout Mountain Caverns, the two caves were not actually connected by any passage. Ruby Falls Cave is the upper of the two and contains a variety of geological formations and curiosities which Lookout Mountain Cave does not have.