and
Mount Agassiz seen from
Bald Mountain The Uinta Mountains are
Laramide uplifted
metasedimentary rocks deposited in an intracratonic basin in southwest
Laurentia during the time of the breakup 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 760 million years old) and consist primarily of
quartzite,
slate, and
shale. These rocks comprise the
Uinta Mountain Group, and reach thicknesses of . 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, includes Uinta Mountain undivided
quartz arenite, overlain by the Moosehorn Lake, Mount Watson, Hades Peak, and Red Shale formations. 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, 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 the 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
Rocky Mountains; it may relate to changing stress patterns and rotation of the
Colorado Plateau. The Green River used to flow into the
Mississippi River to the
Gulf of Mexico, but changed to the Colorado River by going through the Uintas in ways not fully understood. 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 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 to reach over without modern glaciers, and are in fact the highest mountain range in the contiguous United States with no modern glaciers.
Permafrost occurs at elevations above and at times forms large
rock glaciers. Soils in the Uinta Mountains are acidic to varying degrees, in contrast to the neutral or alkaline
pH readings which prevail at lower elevations across most of Utah. Between the summits and ridgelines are wide, level basins with around 500 small lakes. One of the most popular lakes is
Mirror Lake because of its good fishing, scenic views, and easy road access. ==Hydrology==