It was after completing one of my first hikes in the Grand Canyon years ago, as I stood at the rim and gazed at the majestic painting living before me, that I really began to appreciate its wonder. With time, that sense of wonder grew more vivid, and my connection to the canyon more personal. I even felt the canyon move me in the way religion moves fervent believers. During those first visits, I couldn't quite explain why. Here was a destination so quintessentially American, and yet very much for all the world; a place that is so human, and yet it transcends the human experience by billions of years. Only after working on this guide have I come to understand all those things that, for me, make the canyon not just a beautiful place, but a spiritual one.

Each time I've returned to stand on the edge of time, I've been awed by the terraced buttes and mesas rising thousands of feet from the canyon floor and dividing the many side canyons. Early cartographers and geologists noticed similarities between these pinnacles and some of the greatest works done by human hands. Clarence Edward Dutton, who scouted the canyon for the U.S. Geological Survey in 1880 and 1881, referred to them as temples and named them after Eastern deities such as Brahma, Vishnu, and Shiva. François Matthes, who drew a topographical map of the canyon in 1902, continued the tradition by naming Wotans Throne, Krishna Temple, and other landmarks.

The temples not only inspire reverence, but also tell the grandest of stories. Half of earth's history is represented in the canyon's rocks. The oldest and deepest rock layer, the Vishnu Formation, began forming 2 billion years ago, before aerobic life forms even existed. The different layers of sedimentary rock that piled up atop the Vishnu tell of landscapes that changed like dreams. They speak of mountains that really did move before eroding into nothingness, of oceans that poured forth across the land before receding, of deserts, swamps, and rivers the size of the Mississippi -- all where the canyon is now. The fossils in these layers illustrate the very evolution of life. A descent into the canyon is quite literally a walk back in time.

Many of evolution's latest products -- more than 1,500 plant and 400 animal species -- exist at the canyon today. If you include the upper reaches of the Kaibab Plateau (on the canyon's North Rim), this small patch of Northern Arizona encompasses many diverse zones of biological life (associated plants and animals that fall into distinct bands or communities). In fact, climbing from the canyon floor to the top of the North Rim is like traveling from Mexico to Alaska in terms of the biological life you'll see.

The species come in every shape, size, and temperament, ranging from tiny ant lions on the canyon floor to 1,000-pound elk roaming the rims. And for every species, there is a story within the story. Take the Douglas fir, for example. Once part of a forest that covered both rims and much of the canyon, this tree has endured since the last ice age on shady, north-facing slopes beneath the South Rim -- long after the sun-baked rim itself became inhospitably hot.

As much as I like the stories, I also enjoy the unexplained mysteries. The web of ecological cause and effect among the canyon's species is too complicated for any mortal to untangle. It leaves endless questions to ponder, such as, "Why does the agave bloom only once every 20-odd years?" Similarly, the canyon's rocks withhold as much as they tell. More than a billion years passed between the time the Vishnu Schist formed and the Tapeats Sandstone was deposited atop it -- a gap in the geological record commonly referred to as the Great Unconformity. Other gaps -- or unconformities, as they're called -- exist between other layers. And river gravels that would have explained how the canyon was cut have long since washed away.

There's a fascinating human history here, too. The more time I spend inside the canyon, the better I hope to understand the first people who dwelt there. A number of tribes have lived in or around the canyon, and the Navajo, Havasupai, Kaibab Paiute, Hopi, Zuni, and Hualapai tribes still inhabit the region. Before Europeans arrived, they awakened to the colors of the canyon, made their clothes from its plants and animals, smelled it, touched it, tasted it, and felt it underfoot. The Hopi still regard the canyon as their place of emergence and the source to which their dead return. Native Americans have left behind more than 4,000 archaeological sites and artifacts that may be as old as 10,000 years.

I also reflect on some of the first white people who came to this mystical place. The canyon moved them to take extraordinary, if not always productive, actions. I think about the prospectors who clambered through the canyon in search of precious minerals, and then wonder about the ones who stayed here even after their mines proved unprofitable. I wish I could have met icons such as Georgie White, who began her illustrious river-running career by swimming 60 miles down the Colorado River in the western canyon, and Mary E. Jane Colter, the brilliant architect who aspired to create buildings that blended with the landscape, going so far as to grow plants out of the stone roof at the Lookout Studio. I'd still like to meet David Brower, who, as the Sierra Club's executive director, helped nix a proposal to dam the Colorado River inside the Grand Canyon. He did so by running full-page ads in the New York Times that compared damming the canyon to flooding the Sistine Chapel.

Theodore Roosevelt also belongs in this group. During his 1903 visit, the canyon moved him to say, "Leave it as it is. You cannot improve on it. The ages have been at work on it, and man can only mar it. What you can do is to keep it for your children, your children's children ? as the one great sight which every American ? should see." That wasn't just talk. He backed up his words, using the Antiquities Act to declare the Grand Canyon a National Monument in 1908. Congress established Grand Canyon National Park in 1919. I imagine that President Obama, during his 2009 summer visit to the Grand Canyon with his wife and daughters, strongly identified with President Roosevelt's counsel.

Although most visit the park for recreational reasons, the canyon has a daunting, even ominous side. Everyone must negotiate for survival. One look at a river guide's clenched jaw as he or she rows into Lava Rapids will remind you that the canyon exacts a heavy price for mistakes. The most common error is to underestimate it. Try to escape, and it becomes a prison 10 miles wide (on average) and 277 miles long, with walls 4,000 feet high. The canyon's menace, for me, is part of its allure -- a reminder of man's insignificance when measured against nature's greatest accomplishments.

Clearly, you can suffer here, but reward is everywhere. It's in the spectrum of colors: The Colorado River, filled with runoff from the Painted Desert, runs blood red beneath slopes of orange Hakatai Shale. Cactus flowers explode in pinks, yellows, and reds, while lichens paint rocks orange, green, and gray, creating art more striking than in any gallery. It's in the shapes, too -- the spires, amphitheaters, temples, and ramps -- and in the shadows that bend across them before lifting like mist. It's in the myriad organisms and their individual struggles for survival. Most of all, it's in the constancy of the river, which reminds us that, in time, all things move forward, wash away, and return to the earth.

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