GRAND CANYON NATIONAL PARK, Ariz. -- It's so relaxin drifting on a raft down stretches of the Colorado River, beneath the towering red walls of the Grand Canyon, that you can easily slip into that twilight zone between consciousness and sleep. Just about the time you're ready to doze off in the blazing sunshine, however, there comes this sound.
Faint at first, but growing louder, is an ominous rumble that causes all your survival instincts to flash bright red.
"If you hear it but can't see it, watch out," river guide Paul Thevenin says calmly, nodding in the direction of the increasingly deafening din.
Mr. Thevenin, a big man who wears an eagle feather in his pointed cap, has been a boatman for 30 years. His instincts are sharply honed. Based on his experiences on the Colorado, he declares the white-water rapid coming swiftly into view a "three-hander," meaning raft passengers should hold safety ropes with both hands and more for the ride ahead.
Too quickly, the swirling water grabs the raft and hurtles it toward Sockdolager, a rapid with a nasty reputation -- the waves leaping and pounding and frothing against fang-like boulders punctuating the watery chaos.
Over the roar, Mr. Thevenin points to a place just ahead at which all passengers already are staring in wide-eyed fascination.
"That is a hole in the water," he observes, moments before the raft plunges like a roller-coaster car over the brink of the rapid and into a yawning pit-like depression that seems to swallow the raft.
Slamming into the side of the hole, the raft sends a cascade of water into the air, drenching the occupants. They express their exhilaration or dismay in shrieks, cheers, shouts and curses.
It is at times like this that any cameras, hats, sunglasses and other belongings not tied down leap out of the raft and disappear in the battering torrent.
The raft shoots into calmer waters. Heartbeats return to normal.
Almost as an afterthought, Mr. Thevenin remarks, "There are tales of death around here."
Like Stephen Kings of the white-water world, Mr. Thevenin and his fellow guides hold the complete attention of thousands of river-raft travelers each year. They do it with dramatic yarns delivered during leisurely hours on the placid stretches of the Colorado River or with heart-stopping runs through its churning rapids.
Guide John Gray tells one of his favorites, a story about a man named Frank M. Brown who scoffed at the idea of wearing a life jacket during a trip down the river on July 10, 1889. Brown was thrown overboard and drowned, and an inscription marking his death was carved on a rock by Peter Hansbrough, a crew member. Hansbrough drowned in the same fashion five days later.
And, Mr. Gray recalls, there were the honeymooners, Bessie and Glen Hyde, believed drowned Nov. 28, 1928. Their boat, with Bessie's camera and notebook, was discovered floating downstream. Their bodies, Mr. Gray points out in a matter-of-fact tone of voice, were never found.
There are old and new tales of the Colorado River. Guides these days talk at length about the effect on the river of the Glen Canyon Dam, opened in 1964 as a hydroelectric power station six miles from Grand Canyon National Park.
To meet sudden demands for electricity from businesses and households in a six-state region, dam operators release millions of gallons of water into the river each day, causing the level to rise and fall 8 feet or more. Environmentalists charge this manipulation of the river's flow is causing beaches used by rafters and campers to wash away, disrupting wildlife and interfering with the spawning practices of fish. These critics want river levels regulated to protect the Grand Canyon's natural resources and recreation, a $5.5 billion industry in Arizona.
One of the world's seven natural wonders, the Grand Canyon is 277 miles long, at some points 10 miles wide, and more than a mile deep -- an enormous gorge filled with mountain-size stone slabs and buttes.
Carved over a period of 5 million years by the Colorado River, the canyon is a place where the history of the Earth is written in stone, layer by layer, its dazzling colors accentuated by the dramatic glow of sunrise and sunset.
About 4 million people will visit the canyon this year, most arriving by bus or car to glimpse its beauty from the popular Grand Canyon Village on the south rim. The more dramatic view of the canyon is from the bottom, from the shore or surface of the Colorado River.
Under permits issued by the National Park Service, about 20,000 rafters and boaters ply the waters of the river each year, either in private or commercially operated crafts. The park service authorized 963 recreational trips in 1989.
Successful river runners are known locally as river rats.