A new study argues that a proto–Colorado River filled the Bidahochi basin about 6.6 million years ago and later spilled westward—reshaping ideas about how the Grand Canyon formed.
A messy timeline for a world-famous canyon
A proto–Colorado River. a basin. then a spillover
The evidence starts with a detail most readers would miss: sand.. Researchers noticed that sand deposits downstream of the Grand Canyon and sand within the Bidahochi basin share a distinctive look—pink. rounded grains.. That resemblance mattered because it can preserve a fingerprint of transport history.. By dating zircon crystals—durable minerals that can be traced back to their original source rocks—the team reported that the two sand groups appear to have come from rocks across the proto–Colorado River’s watershed.
Misryoum’s key takeaway is not just that a river fed the region, but that the timing and routing may have been different from today. If the Bidahochi basin held substantial water, it would imply that the river’s landscape “network” was reconfigured before the canyon cut its present shape.
# Why the Bidahochi matter is more than local geology
That detail connects the sediment record to a physical question geologists argue about: did the canyon form mainly through gradual cutting. or did dramatic events help trigger the most decisive carving?. Misryoum readers should think of erosion as a competition—channels that capture more water carve faster. and once a new path wins. it can steer the rest of the system for millions of years.
The new hypothesis leans toward spillover being a simpler mechanism than some alternatives.. Researchers acknowledge that their findings do not prove whether the lake overflow involved catastrophic flooding or more gradual spilling.. Still. their model offers a coherent link between where the river’s sediment appears and how it might have begun sculpting a westward route.
# Not everyone agrees—and that’s how science sharpens
Critically, the opponent points to what has not yet been tested: the specific “spillover” scenario’s most important details.. In other words. the sediment match may indicate shared river sources. but the step from “river flowed into the basin” to “this directly caused the canyon’s cutting” still needs additional constraints.
Another perspective complicates the geometry even more.. Misryoum reports that a different critic argues for an older “paleocanyon” already carved across the Kaibab uplift before the proto–Colorado River arrived.. If such a pre-existing channel existed. the river likely would not have pooled to the water levels implied by the new study.. That would weaken the lake-spillover step, even if the sediment story remains plausible.
These disagreements are productive rather than discouraging. They outline what future work must do: test not just whether the river reached the basin, but whether it filled and rose to the right elevations, and whether that timing lines up with when the canyon’s crucial incision began.
Filling a major gap in the river’s journey
Geologists generally agree that the river system was flowing through western Colorado by about 11 million years ago.. Yet the river is thought to have reached the western edge of the Grand Canyon only around 5.6 million years ago.. That leaves roughly five million years where the river’s large-scale route is hard to pin down.
By placing river-derived sediments in the Bidahochi basin about 6.6 million years ago. the study helps locate the river during that ambiguous interval.. That matters because rivers are not static: they reroute as mountains rise, basins open, and tectonics shift drainage divides.. Knowing where the river ran even temporarily can change which hypotheses about canyon formation remain viable.
Misryoum’s interpretation: even if spillover eventually turns out not to be the single dominant driver, the Bidahochi timeline provides a stronger framework for rebuilding the river system’s evolution.
What the new clue could mean next
If future analyses confirm that a lake in the Bidahochi basin routinely overflowed to the west. geologists may refine the “catalyst” phase of canyon incision—tightening when and how erosion accelerated.. If. instead. further evidence favors a pre-existing canyon or a smaller. less influential lake. the field will likely shift from spillover as the main trigger toward alternative mechanisms such as upstream capture or collapse-driven exposure of a new erosional corridor.
Either way, the direction of travel is clear. Misryoum’s takeaway from the latest evidence is that the Grand Canyon’s formation story is becoming less guesswork and more mapped—one basin, one sediment layer, and one dated mineral at a time.
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