2. It is difficult to imagine what the surface topography was like when the cave was forming, yet we know it hasn’t always been the same. The mountains were higher. The streams occupied higher positions in the valleys. The ridges lay in a somewhat different pattern. Now and then stream piracy, or drainage rearrangement, took place when a rapidly eroding stream cut away the ridge separating it from a less active stream. Suddenly the slower stream was diverted into the drainage system of its captor. Both surface and phreatic waters of the aggressive drainage were increased. The flow at the water table speeded up in response. If stream piracy occurred in the drainage overlying the caves, it might have played an important part in cave carving. 3. Nor can we omit the conditions that occurred here during periods of glaciation. Shifting masses of ice and glacial debris characteristically cause damming and rechanneling of water in minor stream valleys. The temporary results are similar to stream piracy. Coupled with this is the great volume of water which drains from melting glaciers. Evidence of partial glaciation in the Siskiyou Mountains lends serious consideration to its effect on early cave development. The whole process might have involved all three of the above situations in varying degrees, for a “geologically sudden” event may take several thousand years. Several distinct levels of cave erosion indicate that the water table moved along at a certain level for a time, then rapidly dropped to a lower course where it was stable for another extended period. This was repeated until it now stands near the level of the River Styx. Successively, the caverns at higher levels were drained and left empty. So as your tour climbs from the cave entrance to the highly developed sections near the Ghost Room, you encounter galleries that are progressively older. The first room inside the entrance, Watson’s Grotto, is the best example we have of a cavern “recently” drained. A word about the River Styx. Above it in several places you can see very smooth walls left by the familiar erosive action of a stream. (See illustration page 14). Most of the cave walls show the more pitted, concave surface left by the acidic dissolving action of phreatic water. The water which produced the main cave system moved much slower than the River Styx, and over a wider area. The stream as we see it did not produce the cave. Rather, the caverns, when drained, left a free flowing course for ground water to channel into. The only true underground streams occur in caves. They are a by-product of the cave-forming process. [Illustration: Smooth-walled erosion of River Styx] _Decoration_