The Grand Canyon may be a collage of differently aged gorges
Arizona’s Grand Canyon runs 277 miles along the Colorado River, up to 18 miles wide and more than a mile deep. New dating fights suggest it is not one young slot but linked segments—some perhaps tens of millions of years old.
The national park, Kaibab forest lands, the Parashant monument, and the Hualapai, Havasupai, and Navajo lands share the rims whose protection Theodore Roosevelt championed. García López de Cárdenas was the first known European to see the gorge, long sacred to Pueblo peoples. It is not the deepest canyon on land, since Nepal’s Kali Gandaki is deeper, but its exposed layers run from the roughly two-billion-year-old Vishnu Schist to the 270-million-year-old Kaibab Limestone, with the Great Unconformity marking a huge gap.
Between 1.25 billion and 730 million years ago the Grand Canyon Supergroup accumulated in shallow seas, beaches, and swamps. Starting about 65 million years ago, the Laramide mountain-building pushed the Colorado Plateau up by 5,000 to 10,000 feet. When the Gulf of California opened 5.3 million years ago, the river’s base level dropped and erosion sped up, and ice-age runoff deepened the cut further. Lava and ash erupted between 100,000 and 3 million years ago at times dammed the river entirely.
Scientists have argued about its age for more than 150 years. Older estimates of 5 to 6 million years were challenged when Victor Polyak’s 2008 cave calcite work pointed to about 17 million years, and Rebecca Flowers’s thermochronometry suggested some reaches were near modern depth 20 million years ago, with a western segment perhaps 70 million years old. The emerging consensus holds that separate segments, including the Hurricane at 50 to 70 million years, formed at different times and later joined.
The North Rim, averaging about 2,400 metres, stays cooler than the South, and summer storms soak both. Rock layers hold two main aquifers, the upper C-aquifer and the deeper R-aquifer, which feeds springs in the canyon walls; many springs mix post-1950 water with much older groundwater. Arizona goldenbush grows only on South Rim cliffs.
Source: Grand Canyon
