In the early 1960's, the nation's environmental movement cut its baby teeth on a fierce battle to stop construction of dams along the Colorado River. Two proposed dams were never built, but Glen Canyon dam, located in an unprotected area, was completed in 1963. Over the next 17 years, water backed up for 186 miles, forming Lake Powell and inundating Glen Canyon and hundreds of miles of side canyons.
The defeat was deeply felt. David Brower, who was executive director of the Sierra Club, called the death of Glen Canyon the greatest disappointment of his life. Edward Abbey, the mischievous author and defender of the natural world, called Glen Canyon the ''living heart'' of the Colorado River and Lake Powell a ''blue death.'' He often spoke of floating a houseboat filled with explosives to the base of the dam to get rid of ''Lake Foul.''
What Mr. Abbey and the Sierra Club couldn't or didn't do nature has now accomplished. A severe Western drought -- some say the worst in 500 years -- is shrinking Lake Powell at the rate of up to a foot every four days. Since 1999, the vast reservoir has lost more than 60 percent of its water.
Glen Canyon is returning. It is open and viewable in much of its former glory. At the confluence of Coyote Creek and Escalante River, where boaters once motored by to see famous rock formations, backpackers now pick their way up a shallow river channel. Fifteen-foot high cottonwoods grow amid thickets of willow, gamble oak and tamarisk. Where fish thrived, mountain lions prowl.
The change may be permanent.
''Short of several back-to-back years with 100-year runoff, Lake Powell will never be full again,'' said Dr. Tom Myers, a hydrologic consultant in Reno, Nev. Downstream users now consume 16.5 million acre-feet of water, but on average only 15 million acre-feet flow into the system each year, he said. Add more than a million acre-feet of water lost to evaporation and it is obvious that only during relatively wet years is it possible to add water.
The struggles over Glen Canyon and the other dams on the Colorado River above the Grand Canyon were among the battles that led to the National Environmental Policy Act, the Endangered Species Act and clean air and water legislation. Among these successes, the dam was a defeat that has not been forgotten. In 1981 the radical environmental group Earth First! unfurled a 300-foot-long sheet of plastic shaped like a crack down the dam's face.
Now, Dr. Richard Ingebretsen, a physician and founder of the Glen Canyon Institute in Salt Lake City, a group dedicated to draining Lake Powell and restoring Glen Canyon to its natural state, says: ''The drought is a godsend. Now is the chance for us to have the national debate we didn't have 40 years ago. With the lake so low, people can see what was lost, the life cycles, the ecosystem. There is a powerful beauty here that can change people's minds.''
The changes are stunning. When it was full five years ago, the lake had 250 square miles of flat water and thousands of miles of fractal shoreline. Each year, two and a half million people came to enjoy vacations with boating, swimming, fishing. The lake was rimmed by a starkly beautiful landscape; filmmakers shot movies like ''Planet of the Apes'' and ''The Greatest Story Ever Told.''
Today the lake is down 129 feet, back to the size it was in 1970, covering 131 square miles. Canyon walls are plastered with a chalky white bathtub ring of calcium carbonate 10 stories high, where the water once reached. Towering benches of silt line the former lake bed. This year 1.8 million visitors are expected.
''The lake is still beautiful,'' said Char Obergh, an information officer for the Glen Canyon National Recreation Area in Page, Ariz. ''People can see more features than ever with the water low.''
Paul Ostapuk, a spokesman for Friends of Lake Powell in Page, said: ''Droughts are a regular part of the Colorado River. The lake draws down and it fills up again.'' In the meantime, he said, families can still get together on the lake for a wonderful time.
In two years, depending on the weather, Lake Powell could reach what hydrologists call inactive pool, meaning the water stored in the lake will not produce enough flow to generate hydroelectric power. A year or two after that, water could drop another 120 feet.
At that point, because of the steepness of canyon walls at the dam, Lake Powell would still have two million acre feet of water spanning 32 square miles, offering continued recreation opportunities.
At that same point, hundreds of miles of side canyons would emerge into sunlight offering backpackers a chance to see what was lost. In an expedition down the Colorado River in 1869, John Wesley Powell provided English names for dozens of features like Tapestry Wall, 1,000-foot-high sand dunes frozen into rock and stained with veils of black desert varnish, and Music Temple, a vast grotto of sinuous stone where a person could hum a note for one second and still hear it resonating 11 seconds later.
Canyons that would be exposed include Dungeon, Labyrinth, Anasazi, Iceberg, Moki, Last Chance, Mystery Rock, Hidden Passage, Twilight and Lost Eden.
Already some features are back, including a stretch of Imperial rapids and a Native American sarcophagus that once held a mummy, now stored in a nearby museum.
But the side canyons are the real miracles of Glen Canyon, said Chris Peterson, executive director of the Glen Canyon Institute who started revisiting the Escalante River at Coyote Creek in 1999. That year the lake was down only a short distance, he said, but a riot of plants had sprung to life overnight.
Dr. David Wegner, an expert on canyon ecology and the president of Ecosystem Management International in Durango, Colo., explained why. First, most side canyons are made of porous Navajo sandstone, which has acted like a huge sponge for 30 years. As the reservoir drops, the stone can't drain as quickly. That water steadily trickles out, feeding the desert ecosystem. Second, the retreating lake leaves sediment loaded with nutrients. Seeds that fall germinate quickly in the shade. Insects, amphibians and birds come back followed by rodents, raccoons, deer and panthers.
Glen Canyon has been called a lost Eden, largely because the conditions are perfect for life. The side canyons, with deep shade and sculptured grottoes, were always the ecological pump for much of the life in the Grand Canyon and beyond, Dr. Wegner said.
Last spring Mr. Peterson and his colleagues began leading small groups down the Escalante River to see the recovery firsthand. This fall, trekkers can walk 15 miles downriver, barefoot, marveling at the sights, sounds and smells.
To everyone's surprise, the bathtub ring is disappearing rapidly. Summer monsoons are washing it away.
There is very little human garbage in the shin-deep river that runs through the old lake bed. On a recent exploration, hikers saw only a plastic bucket and a bottle. The air smells sweet. Clear springs flow out of newly exposed rock. The river bottom is the consistency of confectioner's sugar, a very soft silt that is prone to form pockets of quicksand. As attractive as the exposed canyon is, hiking there can be challenging. It is already possible to explore small side canyons.
Scrambling up and into one of these grottoes is to enter a world of haunting beauty. Out on the river, the air is hot and dry. Suddenly the world turns cool, dark, quiet. Sheer and curved walls of red, orange and ocher-colored rock hold hanging gardens of maidenhair ferns. There are datura often painted by Georgia O'Keeffe, along with orchids, scarlet monkey flowers and cave primrose.
One recent visitor, Alvin Colville, a retired rancher from Del Norte, Colo., first came to Glen Canyon in 1962 when he was 31. ''These side canyons are what called me back,'' he said, hoisting a pack onto his back. ''They're small, cozy, quiet, magnificent. In many places you could touch both walls. The sky was a little blue slot up above.''
Harry Garabedian and Betsey McNaughten of Deering, N.H., were also on the Escalante River recently on a weeklong hiking trip. ''It's beautiful to watch the full moon bounce up over the cliff tops,'' Mr. Garabedian said. But the lakeshore bears witness to recent years. ''Every rock you turn over has toilet paper under it from the years this was a campsite for boats.''
Mr. Peterson said there was one side canyon farther downstream that he could hardly wait to visit on foot. The size of two football fields, overhung with glowing orange and red rock, Cathedral Canyon is perhaps the most famous lost feature in Glen Canyon. To Edward Abbey it was grander than all the cathedrals in Europe. It was a place where he expected to see ''a rainbow colored corona of blazing light, pure spirit, pure being, pure disembodied intelligence, about to speak my name.''
Five years ago it was under 140 feet of water; now, just 18. Last year it had a waterfall five feet high. This summer a monsoon cleared out silt so that the waterfall is now 20 feet high. If it is speaking Mr. Abbey's name it is whispering now, but if the water keeps receding, it may soon be shouting.