60 miles N of Williams; 80 miles NE of Flagstaff; 230 miles N of Phoenix; 340 miles N of Tucson

Whether you merely stand on the rim gazing in awe, spend several days hiking deep in the canyon, or ride the roller-coaster rapids of the Colorado River, a trip to the Grand Canyon is an unforgettable experience. A mile deep, 277 miles long, and up to 18 miles wide, the canyon is so large that it is absolutely overwhelming in its grandeur, truly one of the great natural wonders of the world. Clarence Dutton, a 19th-century geologist who published one of the earliest studies of Grand Canyon geology and who named many of the canyon's prominent landscape features, held the canyon in such reverence that he named land formations for Solomon, Apollo, Venus, Thor, Zoroaster, Horus, Buddha, Vishnu, Krishna, Shiva, and Confucius.

Something of this reverence infects nearly every first-time visitor. Nothing in the slowly changing topography of the approach to the Grand Canyon prepares you for what awaits. You hardly notice the elevation gain or the gradual change from windswept sagebrush scrubland to juniper woodlands to ponderosa pine forest. Suddenly, it's there. No preliminaries, no warnings. Stark, quiet, a maze of cathedrals and castles sculpted by nature.

Layers of sandstone, limestone, shale, and schist give the canyon its colors, and from dawn to dusk, the interplay of shadows and light creates an ever-changing palette of hues and textures. In this landscape layer cake of stone can be read 2 billion years of geologic history, though geologists believe it has taken only 17 million years for the erosive action of the Colorado River to carve the canyon. That the canyon has a complex geologic history is written all over the landscape, which is now an open book exposing the secrets of this region's geology.

The story of the Grand Canyon begins millions of years ago, when vast seas covered this region. Sediments carried by seawater were deposited and, over millions of more years, those sediments were turned into limestone and sandstone. According to the most widely accepted theory, the Colorado River began its work of cutting through the plateau when the ancient seabed was thrust upward to form the Kaibab Plateau. Today, 21 sedimentary layers, the oldest of which is more than a billion years old, can be seen in the canyon. Beneath all these layers, at the very bottom, is a stratum of rock so old that it has metamorphosed, under great pressure and heat, from soft shale to a much harder stone. Called Vishnu Schist, this layer is the oldest rock in the Grand Canyon, dating from 2 billion years ago.

In the more recent past, the Grand Canyon has been home to several Native American cultures, including the Ancestral Puebloans (Anasazi), who are best known for their cliff dwellings in the Four Corners region. About 150 years after the Ancestral Puebloans and Coconino peoples abandoned the canyon in the 13th century, another tribe, the Cerbat, moved into the area. Today, the Hualapai and Havasupai tribes, descendants of the Cerbat people, still live in and near the Grand Canyon on the south side of the Colorado River.

In 1540, Spanish explorer Garcia Lopez de Cárdenas became the first European to set eyes on the Grand Canyon, but it would be another 329 years before the first expedition traveled through the entire canyon. John Wesley Powell, a one-armed Civil War veteran, was deemed crazy when he set off to navigate the Colorado River in wooden boats. His small band of men spent 98 days traveling 1,000 miles down the Green and Colorado rivers. So difficult was the endeavor that when some of the expedition's boats were wrecked by powerful rapids, part of the group abandoned the journey and set out on foot, never to be seen again.

How wrong the early explorers were about this supposedly Godforsaken landscape. Instead of being abandoned as a worthless wasteland, the Grand Canyon has become one of the most-visited natural wonders on the planet, a magnet for people from all over the world. By raft, by mule, on foot, and in helicopters and small planes -- approximately four million people each year come to gaze into this great chasm.

However, there have been those in the recent past who regarded the canyon as mere wasted space, suitable only for filling with water. Upstream of the Grand Canyon stands Glen Canyon Dam, which forms Lake Powell, while downstream lies Lake Mead, created by Hoover Dam. The Grand Canyon might have suffered the same fate, but luckily the forces for preservation prevailed. Today, the Grand Canyon is the last major undammed stretch of the Colorado River.

Named by early Spanish explorers for the pinkish color of its muddy waters, the Colorado River once carried immense loads of silt. Because much of the Colorado's silt load now gets deposited on the bottom of Lake Powell (behind Glen Canyon Dam), the water in the Grand Canyon is much clearer (and colder) than it once was. Today, only when rainstorms and snowmelt feed the side canyons of the Grand Canyon does the river still flow murky and pink from heavy loads of eroding sandstone.

While the waters of the Colorado are now usually clearer than before, the same cannot be said for the air in the canyon. Yes, you'll find smog here, smog that has been blamed on both Las Vegas and Los Angeles to the west and a coal-fired power plant to the east, near Page. Scrubbers have been installed on the power plant's smokestacks, but there isn't much to be done about smog drifting from the west.

Far more visible and frustrating is the traffic congestion at the South Rim during the busy months from spring to fall. With more than four million people visiting the park each year, traffic during the summer months has become almost as bad at the South Rim as it is during rush hour in any major city, and finding a parking space can be the biggest challenge of a visit to Grand Canyon National Park. But don't let these inconveniences dissuade you from visiting. Despite the crowds, the Grand Canyon more than lives up to its name and is one of the most memorable sights on earth.