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Those of us who have trekked from the rim of the canyon to the bottom have a physical, almost visceral sense of the geologic story, which goes back nearly 2 billion years.

An easier, more convenient and more informative approach is to walk along the flat, easy Trail of Time on the canyon’s South Rim.

The 1.3-mile trail, opened about eight years ago, is essentially a geologic timeline. Each meter — 39.37 inches —walked on the timeline signifies 1 million years of the canyon’s geologic history.

Samples of rocks brought to the rim from deep in the canyon are placed along the trail at the point where they appeared in the timeline.

And, virtually all along the trail, walkers get a vast, panoramic view of the mile-deep canyon where the geologic story continues playing out today.

TREK THE TRAIL

Starting just west of the Yavapai Geology museum on the canyon rim, visitors can walk backward in time from today toward the oldest rock in Grand Canyon, Elves Chasm gneiss (1,840 million years old).

Another option is to begin east of Verkamp’s Visitor Center, walking forward in time from 1,840 million years ago toward the youngest rock in the Grand Canyon, Kaibab Limestone (270 million years old).

A National Park Service publication sets the stage for the walk: “Each rock layer represents a period when a particular environment of deposition prevailed. For example, the Kaibab Formation, the rock that makes the canyon rims, is the youngest of Grand Canyon’s layers.

“The Kaibab Formation formed in shallow, warm seas about 270 million years ago, a bit before dinosaurs roamed the earth,� the publication says. “Below the Kaibab Formation caprock, the strata become progressively older� — ending in “basement rocks� that are nearly 2 billion years old.

A geologic cross section of the Grand Canyon, described along the Trail of Time, includes the following layers from youngest to oldest:

• Kaibab Formation — 270 million years ago.
• Toroweap Formation — 273 million years.
• Coconino Sandstone — 275 million years.
• Hermit Formation — 280 million years.
• Supai Group — 315-285 million years.
• Redwall Limestone — 340 million years.
• Temple Butte Formation — 385 million years.
• Muav Limestone — 505 million years.
• Bright Angel Shale — 515 million years.
• Tapeats Sandstone — 525 million years.
• Grand Canyon Supergroup — 1,250-650 million years.
• Vishnu basement rocks — 1,840-1,680 million years.

Compared to these old, old rocks in its walls, Grand Canyon itself is a geologic youngster.

“Excavation of the canyon occurred within the last 6 million years or so,� according to the Park Service. “The question of how the Colorado River evolved its present course is still unresolved, even though geologists have hypothesized for years about how the river first established its path across the plateau and carved the immense chasm.�