A new geological study has found how the Green River cut through the Uinta Mountains and connected with the Colorado River. This major change reshaped river drainage across western North America. The river carved its path long after the mountains formed and active building ended. Scientists looked at river shape, sediment records, and seismic images to understand how this happened. The key was a process deep underground called a lithospheric drip. This means a dense, heavy part of Earth’s crust sank into the mantle beneath the mountains. When this happened, hot mantle rose up, pushing the surface higher by about 450 metres. This uplift happened between 2 and 5 million years ago, well after the mountains rose over 50 million years ago. As the land shifted up unevenly, rivers got steeper and cut deeper valleys, allowing the Green River to cross the range and form the Canyon of Lodore. Surface events like climate or faulting played little role. Instead, this deep Earth movement quietly changed the landscape and river paths. The study, titled “A Lithospheric Drip Triggered Green and Colorado River Integration,” shows that Earth’s mantle forces can reshape landscapes long after mountain building stops, linking deep processes directly to river formation on the surface.