The TRAVELER'S JOURNAL: March sixth, delving the Grand Canyon.

The foundation formed more than a billion years ago. Over aeons, water and wind slathered on thick layers of sandstone, shale, limestone and magma. Great inland seas seeped away, and tectonic tilts pushed up mountains, which erosion filed down to a plateau. Just six million years ago, streams converged into a mountain draining torrent, a fluvial chisel that, aided by rain, wind and ice, carved a gorge 275 miles long, 15 miles wide and over a mile deep.

Though inhabited well before recorded history began, the gorge's first documented descent wasn't until 1869, when John Wesley Powell became a river runner. For decades after, the yawning chasm was regarded as a formidable travel barrier that offered little in the way of material wealth. Then geologists realized the vast excavation revealed a calendar of Earth time. Artists and adventurers joined in, and the canyon became a place to seek out rather than shun.

In the last century, the great chasm and its side canyons have become Grand Canyon National Park and a World Heritage Site visited by millions a year. Each of them takes away a personal vision, but all are shaped by the hugeness of light and sky, the baroque fugue of form and color, the rush of wind and silence, the shrinkage of human presence in the face of nature's transcendence.

With top photos and topo maps, the March issue of the magazine, National Geographic Traveler, a supporter of our program, presents the Essential Grand Canyon. A panel of six canyon cognoscenti cover it rim to rim, top to bottom and through the ages.