Rivers usually take the easiest path. However, in northeastern Utah, the Green River carves through tough limestone and sandstone at Split Mountain instead of flowing toward softer rocks nearby. This unusual route, spanning over 100 miles across the Uinta Mountains, has puzzled geologists for more than a century.
The Uinta Mountains, reaching heights of about 13,000 feet, began forming around 50 million years ago. In contrast, the Green River’s current path is much younger—only about 2 to 8 million years old. This timing gap has led to various theories about the river’s origins.
In 1869, geologist John Wesley Powell camped by the river and suggested that the Green River might have existed before the mountains, creating its channel as they rose around it. He called this a “superposed stream.” His observation stressed that the river carved its own path through the rock.
However, new research questioned Powell’s idea. Since the mountains are much older than the river’s course, experts like Adam Smith from the University of Glasgow suggest that it can’t be as simple as the river predating the mountains. Smith noted the strange route of the river, stating, “It’s such a weird path.” He backed this up with evidence showing that if erosion by another river created this channel, we would see similar canyons in other mountain ranges, which we do not.
Other hypotheses include one where sediment buildup allowed the Green River to flow over the mountains temporarily. Yet with the steep walls of the Canyon of Lodore nearly 2,300 feet high, this notion falls flat according to Smith, who indicates the necessary sediments aren’t present.
Recent research has introduced a fresh idea known as “lithospheric drip.” This concept suggests that parts of the mountains sank before bouncing back, allowing the Green River to flow across them. Smith describes this as “the path of least resistance.” This process occurs where the Earth’s crust meets the mantle, and heavy minerals sink, dragging the crust down until the blob breaks off, causing an uplift.
A study published in the Journal of Geophysical Research highlighted that this kind of drip has created uplift patterns in other mountain ranges, like the Andes. Smith’s team utilized seismic imaging to uncover a deep anomaly beneath the Uinta Mountains resembling an ancient lithospheric drip.
By examining seismic data, they discovered a blob about 120 miles deep that seemed to match the characteristics of a lithospheric drip. They estimate that this blob likely detached between 2 and 5 million years ago, corresponding with when the Green River began to carve through the mountains.
With the landscape lowered, the river effectively seized the opportunity to create its own course, cutting into the rock and forming dramatic features like the Canyon of Lodore. Experts not involved in the study, like Mitchell McMillan from Georgia Tech, endorse the lithospheric drip theory as a plausible explanation for the river’s unusual path. He commended the research for linking surface observations with deep Earth processes, showcasing a valuable method for understanding geological phenomena.
