The Problem
The Green River's path through Utah's 13,000-foot Uinta Mountains has defied geological logic for 150 years. Rivers don't flow uphill through mountain ranges—they find paths around them. Yet the Green River carved a 700-meter canyon straight through peaks that predated the river by 42 million years.
The Solution
Researchers from universities in the UK and US have identified the likely cause: lithospheric dripping. Published in Journal of Geophysical Research: Earth Surface this month, the study synthesizes seismic imaging, river network modeling, and crustal measurements to explain what happened.
A dense section of Earth's mantle and lower crust beneath the Uintas became heavy enough to break away and sink 2-5 million years ago. As it descended, it pulled the mountains down temporarily—making them the path of least resistance for the Green River. The river cut through, establishing the Canyon of Lodore and eventually linking to the Colorado River system.
When the drip broke off completely, the mountains rebounded upward, leaving the river locked in its channel.
The Evidence
Seismic imaging revealed a cold anomaly 200 kilometers below the surface—the broken-off drip segment, 50-100 km across. The crust beneath the Uintas is several kilometers thinner than expected, consistent with dense material having drained away. Surface uplift calculations matched observed elevations to within 400 meters.
Why It Matters
This merger altered North America's continental divide—the line separating Pacific-bound rivers from Atlantic-bound ones. It created new habitat boundaries that influenced wildlife evolution across the region.
The methodology demonstrates how surface observations can decode deep mantle processes. Mitchell McMillan from Georgia Tech, not involved in the study, called it "a valuable demonstration of such an approach."
The Alternatives
Two competing theories don't hold up: that the river predated the mountains (contradicted by geological records), or that sediment buildup allowed the river to overtop the range (insufficient sediment height relative to canyon depth).
History suggests that when multiple data sources converge on a single explanation after decades of debate, the explanation usually sticks. We'll see.