A river cut through Utah’s mountains due to a sinking crustal mass that lowered the land, then rebounded to lock in the river’s path.

A new study explains how Utah’s Green River carved through the Uinta Mountains despite geological expectations. Researchers led by Adam Smith of the University of Glasgow found that a lithospheric drip—where dense crustal material sank into the mantle—temporarily lowered the mountains, allowing the river to cut through. When the dense mass broke off, the land rebounded, locking the river’s path. Seismic imaging revealed a deep, cold anomaly beneath the range, supporting the theory. The findings, published in the Journal of Geophysical Research: Earth Surface, challenge older ideas and suggest similar processes may shape other puzzling landscapes worldwide.