Geology and Climate

Structurally, Castle Valley is part of a large collapsed salt anticline that includes Paradox Valley to the southeast on the other side of the La Sal Mountains.

Over 300 million years ago, thick layers of salt were deposited in the area under marine conditions. These layers were subsequently buried under sediments. The entire area was lifted in the late Tertiary to create the Colorado Plateau. Over time, erosion of the sedimentary layers allowed ground and surface water to contact and dissolve the salt layers. Overlying rock strata collapsed and eroded, forming Castle Valley. High angle fault systems exist on both sides of Castle Valley as a result of the collapse process.

Much later, a mere 24 million years ago, the La Sal Mountains and Castle Valley's Round Mountain rose up as a result of underground volcanic activities. Officially called laccoliths, the La Sals are a kind of volcanic blister created as rising magma was not released through the surface but forced its way into overlying sedimentary layers, lifting them up by over 6,000 feet.

The Valley floor has been filled over eons by sedimentary processes, mass movement and stream deposits. And, as residents well know, these processes continue today when rainstorms cut through some areas and spread alluvium onto the Valley floor (see Flood Hazard Map -- may take a little while to load up).

The total Valley is approximately 8 miles long and 3 miles wide (slightly larger than Manhattan Island). It drops from nearly 6000 feet to about 4200.

The average precipitation for Castle Valley is about 9 inches, although the higher elevations of the Valley tend to get more rain and snowfall. Similarly, maximum and minimum temperatures vary from the higher elevations to the lower elevations. (In winter, the lower Valley can be the coldest area!) Average daytimes highs range from the high nineties in mid-summer to the mid-thirties in early winter.

Human History

Fremont and Ute people were in the area of Castle Valley long before white settlers arrived in the region. Arrowheads and shards have been found throughout the Valley, particularly around the unique "stone pile" located on the grounds of the old ranch house. Some claim this was a meeting place.

 A monument located above Castle Valley to the southwest marks the spot of the 1881 Pinhook battle, in which eight posse members, two Moab cattlemen, and possibly as many as two dozen Native Americans lost their lives in a confrontation over land and misinformation.

 When Castleton and Miner's Basin were "real towns" in the late 19th and early 20th centuries, Castle Valley was a farming area. Brothers Mat and John Martin owned large spreads in the Valley, and Mat's son, born in 1886, was probably the first non-Native American child born here. The Martins' sister was married to Tom Parriott, who was a road worker and mail carrier and gave his name to Parriott Mesa.

 Up until the 1920's, the focus of the Castle Valley farming community was towards Castleton, then a small mining and sheepherding boomtown, and the post office/general store in Richardson, an outpost in Professor Valley. With the decline of Castleton and the disappearance of Richardson, Castle Valley's isolation led to the selling and consolidating of land into large ranching parcels. The "old ranch house" near the large cottonwood tree was the homestead of what eventually became the McCormick Ranch.

 The Carlsberg Development Corporation bought the McCormick ranch and got approval for the plat of Castle Valley River Ranchos in 1973. The sale of lots began in 1974.

In the early years, as an unincorporated community in Grand County, the Castle Valley River Ranchos Property Owners Association was critical to governance. In 1985, the Town of Castle Valley was officially incorporated.

Currently 

The Town of Castle Valley is approximately 8 square miles. While much of the Town consists of the platted River Ranchos and the separate Upper 80, there is a significant portion of the Town that is undeveloped. In 2005, Utah State School and Institutional Trust agreed to a land exchange that transfered ownership of a large porton of land adjacent to the incorporated Town of Castle Valley to the United States Bureau of Land Management. See Official Town Map.

 The average elevation of the Town of Castle Valley is about 4800 feet. According to the 2020 census population 352, the median age in Castle Valley is a relatively high 63.4 years and the median income is $74,474. Education levels are very high: 96% of the adult population graduated high school or higher and approximately 58.9% have college degrees. 100% of the population is classified as White Non-Hispanic.