Physiographic Provinces

Physiographic Regions of Utah

Utah is comprised of parts of three major physiographic provinces, each with characteristic landforms and geology. These include the Basin and Range Province, the Middle Rocky Mountains province, and the Colorado Plateau province.

An overlapping of two of these provinces essentially forms a fourth physiographic region. The Basin and Range-Colorado Plateau transition zone extends through central and southwestern Utah, and contains physiographic and geologic features similar to both the Basin and Range and Colorado Plateau Provinces.

Basin and Range Province

The Basin and Range Province is noted for numerous north-south oriented, fault-tilted mountain ranges separated by intervening, broad, sediment filled basins.

The mountain ranges are typically 20 to 50 km (12 to 31 mi) apart, 45 to 80 km (28 to 50 mi) long and are bounded on one, or sometimes two sides by high-angle, commonly listric, normal faults.

Typical mountain ranges are asymmetric in cross section, having a steep slope on one side and a gentle slope on the other. The steep slope reflects an erosion-modified fault scarp and the range is a tilted fault block.

Rocks within the Basin and Range vary widely in age and composition. Older rocks consist mostly of a variety of Mesozoic and Paleozoic sedimentary units and their metamorphic equivalents.

Proterozoic-age rocks have limited exposures in the region. Cenozoic volcanic rocks and valley-fill units generally overlie the sedimentary and metamorphic rocks. Valley-fill deposits consist mostly of late Cenozoic lakebeds and alluvium as much as 3,000 m (10,000 ft) thick.

Middle Rocky Mountains Province

The Middle Rocky Mountains province in northeastern Utah consists of mountainous terrain, stream valleys, and alluvial basins.

It includes the north-south trending Wasatch Range, comprised mainly of pre-Cenozoic sedimentary and Cenozoic silicic plutonic rocks, and the east-west trending Uinta Mountains, comprised mainly of Precambrian sedimentary and metamorphic rocks.

Colorado Plateau Province

The Colorado Plateau province is a broad area of regional uplift in southeastern and south-central Utah characterized by essentially flat-lying Mesozoic and Paleozoic sedimentary rocks.

Scattered Tertiary and Quaternary volcanic rocks are present on the western margin of the Colorado Plateau in south-central Utah, and some Tertiary intrusive bodies are present in southeastern Utah.

Plateaus, buttes, mesas, and deeply incised canyons exposing flat-lying or gently warped strata distinguish the Colorado Plateau of southeastern Utah. Bedrock units are spectacularly exposed, while surficial deposits are sparse.

Basin and Range – Colorado Plateau Transition Zone

The Basin and Range-Colorado Plateau transition zone is a broad region in central Utah containing structural and stratigraphic characteristics of both the Basin and Range Province to the west and the Colorado Plateau province to the east.

The boundaries are the subject of some disagreement, resulting in various interpretations using different criteria.

Essentially, extensional tectonics of the Basin and Range has been superimposed upon the adjacent coeval uplifted blocks of the Colorado Plateau and Middle Rocky Mountains.

The result is that block faulting, the principal feature of the Basin and Range, extends tens of kilometers into the adjacent provinces forming a 100-km- (62 mi) wide zone of transitional tectonics, structure, and physiography.