Long after tectonic plate movement has created mountains, forces such as weather and river erosion can continue to shape a landscape. One such landscape is the Colorado Plateau, which spans more than 336,000 square kilometers (83 million acres) across four states and encompasses iconic sites such as the Grand Canyon and Arches National Park.

Dramatic gorges such as these are created when a river incises into the rock below over millions of years. The rate of river incision in the Colorado Plateau has varied over time and is not well understood.

Natalie Tanski and colleagues looked at two reaches of the Colorado River to determine how and why incision varied during the Pleistocene, dating fluvial gravel deposits that form river terraces, which are steplike features that mark the former floors of river valleys. Their study is published in the journal AGU Advances.

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The researchers found that in the Moab region of the central Colorado Plateau, river incision paused from 1.8 million years ago to about 350,000 years ago. This pause was followed by a period of rapid incision lasting to the present, during which the river systems carved 200 meters deeper into the plateau. These shifts can be linked to base-level changes as the Colorado River established its path, eventually contributing to the shape and iconic chasm of the Grand Canyon and its tributaries.

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