
For over a century, scientists have puzzled over why the Green River appears to flow “uphill” through the Uinta Mountains in Utah before eventually joining the Colorado River. A new study suggests the answer lies deep beneath the Earth’s surface. A team of geologists led by Adam Smith of the University of Glasgow reports that the river didn’t actually reverse direction; instead, the land beneath it moved. According to the study, published in the Journal of Geophysical Research, the root of the Uinta Mountains became unusually dense over millions of years. That extra weight caused part of the mountain’s deep lithospheric root to slowly sink downward into the mantle, pulling the surface of the region lower with it. When the dense root finally detached around two to five million years ago, the mountains began to rise again, but by then, the river had already locked in its seemingly downward course. The result is an optical illusion: a river that looks like it flows uphill, even though gravity was working the same way all along.



















