Synthesis of the work of many geologists has revealed the nature and history of a very large anticline under two large structural depressions, the Sanpete Valley and the Sevier Valley in central Utah. This anticline is 65–70 miles long and has a structural relief of possibly 15,000–20,000 feet. It is east of and parallel to the eastern limit of mid-Cretaceous folding in Utah and is in the midst of the northern High Plateaus of Utah.

The fold had its inception no later than the early Laramide orogeny and was probably initiated by compression. Subsequently, however, the highly mobile Arapien Shale of Jurassic age flowed toward the axial area because of renewed compression as well as geostatic pressure. As a result, the relatively very incompetent Arapien has been topographically high almost constantly or very frequently exposed since its exposure following the early Laramide orogeny. As a further result, all of the stratigraphic units, with possibly one exception, deposited in the area since the early Laramide orogeny are known to overlap the Arapien core, and many locally dip away from it.

The Redmond Hills anticline is a somewhat similar but smaller structure and has been inferred to have a comparable origin and history.

Some of the unconformities in the immediate vicinity of Sanpete and Sevier valleys, which were previously interpreted as indicators of compression, may more correctly reflect the upwelling of the Arapien Shale and the attendant tilting of the overlapping strata.

First Page Preview

First page PDF preview
You do not currently have access to this article.