Uinta Mountains - Geology

Geology

The Uinta Mountains are Laramide uplifted metasedimentary rocks deposited in an intracratonic basin in southwest Laurentia during the time of the break up of the supercontinent Rodinia. The marine and fluvial metasedimentary rocks in the core of the Uinta Mountains are of Neoproterozoic age (between about 700 million and 800 million years old) and consist primarily of quartzite, slate, and shale. These rocks comprise the Uinta Mountain Group, and reach thicknesses of 4 to 7.3 kilometres (13,000 to 24,000 ft). Most of the high peaks are outcrops of the Uinta Mountain Group. Many of the peaks are ringed with bands of cliffs, rising to form broad or flat tops. The mountains are bounded to the north and south by reverse faults that meet below the range, on the north by the North Flank fault and on the south by the Uinta basin boundary fault.

The Uinta Mountain Group from oldest to youngest comprises Uinta Mountain unidivided quartz arenite, overlain by the Moosehorn Lake formation, the Mount Watson formation, the Hades Peak formation, and the Red Shale formation. The flanks of the east-west trending Uinta Mountains contain a sequence of Paleozoic and Mesozoic strata ranging from the Cambrian Lodore Formation to the Cretaceous Mancos Shale Formation, all of which have been tilted during the uplift of the mountain range.

The uplift of the range dates to the Laramide orogeny, about 70 to 50 million years ago, when compressive forces produced high-angle reverse faults on both north and south sides of the present mountain range. The east-west orientation of the Uintas is anomalous compared to most of the ranges of the northern Rocky Mountains; it may relate to changing stress patterns and rotation of the Colorado Plateau.

The high Uintas were extensively glaciated during the last ice age, and most of the large stream valleys on both the north and south sides of the range held long valley glaciers. However, despite reaching to over 13,500 feet (4,110 m) in elevation, the climate today is sufficiently dry that no glaciers survived even before the rapid current glacial retreat began in the middle nineteenth century. The Uintas are the most poleward mountain range in the world reaching over 4,000 metres (13,000 ft) without glaciers and are in fact the highest mountain range with no glaciers in the United States. Permafrost occurs at elevations above 10,000 feet (3,000 m) and at times forms large rock glaciers.

In between the summits and ridgelines are wide, level basins, with some 500 small lakes. One of the most popular lakes is Mirror Lake because of its good fishing and scenic views.