On the Paradox Valley

First Light

I've mentioned that I visit the Paradox Valley in the Castle Valley area of Utah for photography. I state on my photography site (buzzshawphoto.com) that I do my 'photography through a geologist's eye'. To me, this describes what I do. I learn the historical geology of an area as I go there to do my work. In these reflections, I plan on presenting the images I capture, the process I go through, and the geologic history that formed the features. Sometimes I'll be posting what is literally just a rock, and I'll always take the time to explain it. What I'll present to you will be summaries of my learning more about what I'm seeing. I hope you find this interesting and learn a little bit more. Which is what I am doing, so join me.

I've built an information store of the geology of the Colorado Plateau in Google's NotebookLM. I asked it to provide an overview of the Paradox Valley. I've presented that background below for your edification. I always liked that word, edification.

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Paradox Valley is a distinctive geological basin situated primarily in western Montrose County, Colorado, and forms part of the larger Paradox Basin, which extends into southeastern Utah and southwestern Colorado. The valley's name originates from the "apparently paradoxical course" of the Dolores River, which cuts perpendicularly across the valley floor instead of flowing along its length, a feature that made irrigation difficult. This unusual fluvial geomorphology is also observed in the Moab Valley (Spanish Valley) with the Colorado River.

Geological Formation and Features
• Formation as a Collapsed Salt Anticline
◦ Paradox Valley is fundamentally a collapsed anticline, a type of geological fold formed through a process known as salt tectonics.
◦ Approximately 300 million years ago, during the Middle Pennsylvanian period, thick layers of salt were deposited in a restricted marine basin setting within the Paradox Basin. This basin was an asymmetric downwarp on the southwestern flank of the Uncompahgre uplift, created by the same tectonic forces that raised the Ancestral Rocky Mountains.
◦ Under immense pressure from overlying sediments, the less dense salt flowed plastically. High pressures from the northeast caused these salt deposits to be deflected upwards against a buried fault-block ridge, forming a salt dome. Over millions of years (approximately 150 million years), groundwater dissolved the underlying salt beds, leading to the collapse of the overlying rock strata and the formation of Paradox Valley. This slow process allowed the Dolores River to maintain its original course across the deforming landscape.
• Paradox Formation
◦ The Paradox Formation, a geological unit named after exposures in Paradox Valley, comprises salt, gypsum, anhydrite, shale, sandstone, and limestone.
◦ This formation is characterized by at least 29 sedimentary cycles, where normal marine rocks (like limestone and shale) transitioned to evaporite deposits as sea levels dropped and the basin became cut off from the open ocean.
◦ Potash (sylvite) precipitates when potassium concentrations are about 90 times that of normal seawater, indicating highly hypersaline conditions during specific cycles.
• Dimensions and Topography
◦ Paradox Valley generally trends northwest-southeast, measuring approximately 3 to 5 miles (4.8 to 8.0 km) wide and 25 miles (40 km) long. One source describes it as the biggest of several unusual valleys, at 30 miles long and 3 miles wide.
◦ Elevations on the valley floor range from around 5,000 feet (1,500 m) near the Dolores River to nearly 6,000 feet (1,800 m) at its southeastern end.
◦ It is bounded by steep parallel sandstone and shale walls. The La Sal Range is visible to the northwest in Utah.
• Underlying Salt Walls
◦ Near-surface salt beds up to 14,000 feet (4,300 m) thick still underlie Paradox Valley. Geophysical data and well drilling have confirmed the existence of massive salt walls beneath these long valleys, with vertical sides documented up to 4 km (over 14,000 feet) thick. These salt walls are responsible for the steep dipping angles of the overlying rock formations.
Natural Resources and Human Activity
• Mineral Resources
◦ The Paradox Basin is well-known for its abundant natural resources, including oil and gas, copper, manganese, uranium, and vanadium.
◦ Historically, carnotite mines near Paradox Valley were recognized in 1913 as the source of "the greatest radium ore deposits in the world". Uranium and vanadium production continued for most of the 20th century after radium production ceased in 1922.
◦ Potash (potassium chloride), a valuable commodity, is mined from sylvite deposits within the Paradox Formation.
◦ As of 2009, there was a proposal to build a new uranium mill in Paradox Valley, which would be the first in the United States in over 25 years.
• Salinity Control Project
◦ The Dolores River naturally picks up a substantial amount of salt, estimated at 100,000 to 200,000 tons annually, as it flows through Paradox Valley.
◦ To mitigate this, the United States Bureau of Reclamation operates the Paradox Valley Unit (PVU). This salinity-control project collects saline groundwater from 12 shallow wells along the Dolores River, dilutes the brine, and injects it 14,000 to 16,000 feet (4,300 to 4,900 m) deep into Precambrian and Paleozoic rocks. The PVU removes approximately 113,000 tons of salt annually.
◦ The deep-well injection program associated with the PVU has caused thousands of earthquakes in the area.
• Human History
◦ Historically, Paradox Valley was within the domain of the Ute tribe. However, squatters began grazing cattle in the valley by 1877, leading to the forced displacement of the Utes by 1881.
◦ The discovery of copper in the mid-1890s and subsequent radioactive material mining brought an influx of settlers.
Relation to the Colorado Plateau
The Paradox Basin is a significant part of the Colorado Plateau, a vast physiographic region in the southwestern United States centered on the Four Corners area (Utah, Colorado, Arizona, New Mexico). The Colorado Plateau is known for its remarkable crustal stability and flat-lying sedimentary rocks that have been gently uplifted. The extensive salt deposits and salt tectonics within the Paradox Basin have played a crucial role in shaping the unique and dramatic landscapes, including arches, grabens, and needles, seen across this part of the Colorado Plateau.