Overview
- The Science study, published Thursday, argues an ancestral Colorado River filled the Bidahochi basin by about 6.6 million years ago and later overtopped the Kaibab uplift around 5.6 million years ago to enter what became the Grand Canyon.
- Researchers used uranium–lead dating of tiny zircon grains to match Bidahochi sands to known Colorado River sediments, creating a clear sediment “fingerprint” that traces where the sand came from.
- Supporting clues include thicker sediment piles over time, strontium isotope ratios that point to Colorado River water, ripple marks showing a strong river entering a lake, and fossils of large fast‑water fish.
- The work helps close a five‑million‑year gap in the river’s history and tracks its downstream link to the Gulf of California around 4.8 to 5 million years ago, marking its shift to a continent‑spanning river.
- Several geologists accept that river water reached the basin but say the lake’s size, any over‑the‑top height, and the exact spill path remain unproven, which leaves room for tests that could confirm or revise the scenario.