From: The Matrix 2 - by Valdamar Valerian
It is interesting to note that between Sheridan and "The Medicine
Wheel" is Tongue River Cave. Spiraling down into the depths of the earth
from an entrance 400 feet above the cascading river is an enormous
limestone Cavern extending more than 6,700 feet into the Subterranean
World. Here lies an extensive, far from fully explored, network of
tunnels, and rooms of varying sizes. Feu: inside we find waterfalls and
an Underground River.