Canyonlands National Park - Grabens

The grabens in the Needles District of Canyonlands National Park are a system of linear collapsed valleys caused by the movement of underlying salt layers toward the Colorado River canyon. The grabens begin near the Confluence of the Green and Colorado rivers and run roughly parallel to Cataract Canyon for 25 km, veering slightly west before they end. Graben is a German word meaning ditch or grave. In the geologic sense it is a collapsed or down-dropped block of rock that is bordered on its long sides by faults. Grabens are normally associated with "horsts," which are the up-thrown blocks of rock. In German, Horst means aerie, referring to the high nesting sites of predatory birds.

The processes that led to the development of the grabens began approximately 300 million years ago in the Pennsylvanian period with the deposition of evaporates (salts) in a shallow inland sea. These deposits, known as the Paradox member of the Hermosa Formation, were later covered by the limestone layers of the upper Hermosa and Rico formations. In the Needles District, the Paradox layer can be 3,000 to 5,000 feet thick.

Sediment from a variety of environments continued to accumulate on top of these layers for millions of years. Approximately 60 million years ago, a tectonic plate collision called the Laramide Orogeny created the Rocky Mountains. Shortly after, a regional upwarp called the Monument Uplift caused the sedimentary layers in the Needles to tilt gradually westward. This event also formed joints, or long parallel fractures in the rock, throughout the Needles. In the vicinity of the grabens there are two joint sets: one trending roughly northeast to southwest, and one trending northwest to southeast. Some of these joints became the faults that border the grabens.

Necessary Ingredients