We follow Marion and his ego downriver, plodding along the muddy bank before cutting to an upper-level passage on the right. "We'll have to crawl some this way," Smith says, "but if we went the other way, you'd have to wade through chest-deep water in places. Besides, I left a rope up here that I need to fetch."
Rumbling Falls is not a terribly difficult cave: It just keeps going and going. "The first mile isn't that remarkable," Steve Alvarez, another photographer, had said at the top of the pit, "but by the time you hit the third and fourth miles, it's pretty amazing."
Gary Chambers, a member of Smith's mapping group, sees it differently: "It's the death of a thousand cuts."
Although the passage size remains large, and Smith has been leading us down the best path, every step requires vigilance. Movement in a cave is a matter of constant problem-solving. It's much like steering a four-wheel-drive truck down a bad mountain road. The difference is that in a cave your feet, knees, and hands take the place of knobby tires.
My choices are easy: I crawl where Smith crawls, climb where he climbs. His endurance and determination are unmatched. Despite a bad back, fading eyesight and other infirmities of age, he is impervious to pain, unable to sit still with passage ahead of him.
Eventually we exit the crawlway and work our way back to the river in a spacious junction hall, Smith sprinting ahead. For the next half mile the trip becomes a muddy slog. As we move along the rocky path above the river, we hit an obstacle I dub the Butter Horse. It's the only way forward: a piece of limestone about the size, shape and height of a horse, with deep holes to either side. It's covered in at least four inches of slick mud. If you're fast and brave, you can cross its spine in three or four strides. I choose instead to straddle the rock, moving forward in little hops on my hands. At the far end I slip down a muddy chute, taking care to keep a boot forward to brake the slide because using my shin or hand would be enormously painful.
Just beyond the Butter Horse I catch up to Smith, who is waiting for me on a high ledge with a commanding view of the river. "Look at this," he says. He gestures toward the winding stream and the darkness beyond in a way that reminds me of a painting I once saw of Lewis and Clark. Smith recalls a previous visit during which he reached this point at the end of a long trek and called it a day. "I've never in my life turned around with that much virgin cave ahead of me," he says.
While Smith and his crew were surveying, they weren't exactly sharing. As the Nashville Grotto (chapter) of the NSS prepared to fight the state to keep effluent out of the small, known caves down Dry Fork Creek, its members remained in the dark about Rumbling Falls. At one point Hutchison, who had found the cave, asked a member of Smith's survey team how the mapping was going. " Marion's mapping miles and miles of crawlway" was the answer—true, but nothing was said about the many more miles of gigantic walking passage being mapped. The team feared that if it revealed the extent of Rumbling Falls, hordes of other explorers would descend.
On their survey trips, some of which lasted days, Smith and his crew steadily pushed their way into new chambers and passages that less dedicated cavers might have explored without mapping. There was, for example, Gary's Chamber (named after Gary Chambers), approximately 370 by 150 feet, with a 120-foot-high ceiling; and Birthday's Bonanza (found during the week of Swartz's and Smith's birthdays in September 1999), an 800-foot-long chamber with walls 200 feet apart. "A lot of people will tell you Marion Smith is greedy," Smith told a reporter who later questioned him about the secrecy. "Well, we were greedy. It was a gift from the caving gods late in my career."
But as news of the sewage plant and the Nashville Grotto's fight against it spread, many members of the survey team felt they would have to go public. Smith argued for keeping the cave a secret. Finally, in March 2000, Jack Thomison, a member of the survey crew, convinced Smith that it was time to act. Smith met privately with officials of the Tennessee Department of Environment and Conservation (TDEC) to describe the cave and his concerns about its future.