This Uinta Mountains of Utah are distinctive for the ancient (roughly 700-million-year-old) sedimentary rocks that are exposed throughout the range. As such, they are part of a larger system preserved in small areas throughout the southwestern United States that contain vast quantities of sediment eroded from roughly one-billion-year-old rocks.
Because very few rocks of this age are found in the Southwest, it has been unclear where this vast quantity of sediment originated. Mueller et al. conducted U-Pb age determinations on the mineral zircon using an ion microprobe, hafnium isotopic analyses using a laser ablation technique (also on zircons), and potassium-argon analyses on individual mica crystals to determine the source of the sediment. They determined that there were two primary sources. One was local and derived from the adjoining ancient rocks of Wyoming (2.5 billion years old), and the other was apparently from the area under the present Appalachian Mountains of eastern North America. This implies an extensive river system was present 700 million years ago that carried sediment from a Himalayan-type mountain range in the region of the current Appalachian Mountain system thousands of kilometers to the modern American Southwest. This river system persisted for at least 200 million years and was eventually disrupted during the separation of nascent North America from the supercontinent Rodinia.-Geological Society of America
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