The Green River in Utah’s Uinta Mountains follows a perplexing path, and a team of scientists think “lithospheric drip” is the culprit.

The western U.S. is a geologists' dream, home to the Rocky Mountains, the Grand Canyon, active volcanoes and striking sandstone arches. But one landform simply doesn't make sense.

This aligns with preexisting estimates of when the river probably carved through the Uinta Mountains—creating a canyon that today is 2,297 feet (700 meters) deep—and joined the Colorado system. In ...