Rock Canyon near Provo, Utah County: A Geologic Field Laboratory (original) (raw)
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Geologic map of the Willow Springs Quadrangle, Sevier and Emery County, Utah
The Willow Springs quadrangle lies along the west edge of the Colorado Plateau physiographic province and the east edge of the High Plateaus, a transition zone between the Colorado Plateau to the east and the Basin and Range Province to the west, and is in the Colorado River drainage basin. Exposed bedrock ranges from Middle Jurassic to Late Cretaceous in age and includes (in ascending order) the Entrada Sandstone, Curtis Formation, Summerville Formation, Morrison Formation, Cedar Mountain Formation, Dakota Formation, and Mancos Shale, and is more than 3800 feet (1160 m) thick. The rocks of the quadrangle dip gently northwestward from the large San Rafael Swell anticline into the Fish Lake Plateau syncline. This pattern is interrupted by two folds that are parallel and plunge northwestward—the Salvation Creek syncline and the Last Chance anticline. The strata dip northeastward and northward on the shared limb of these two folds in the southern third of the quadrangle, mostly from 10 to 20 degrees. A Pliocene tephrite dike cuts Jurassic strata in the southwest part of the quadrangle. Quaternary surficial deposits of Holocene to Pleistocene age include varieties of alluvium, mass-movement deposits, mixed pediment-mantle and colluvial deposits, and mixed eolian and alluvial deposits. These deposits cover extensive areas in the northwest quadrant, Blue Flats, and Last Chance Desert parts of the quadrangle. Some of these deposits are associated with landslide and debris-flow hazards. The Dakota Formation and Ferron Sandstone Member of the Mancos Shale contain coal deposits, and bentonite mud is mined in the quadrangle from the Brushy Basin Member of the Morrison Formation. Morrison Formation outcrops are generally littered with chert (agate and jasper). The Cedar Mountain Formation has yielded important vertebrate fauna including dinosaurs, the earliest North American snakes, frogs, early mammals, and the earliest North American marsupial. Even though exploration wells drilled into the Last Chance anticline were dry, oil and gas possibilities in the quadrangle are classified as favorable.
The Moab Fault is a 28 mi (45 km) long, salt-related, normal fault of about 3,100 ft (950 m) maximum surface throw. The fault cuts a Pennsylvanian to Cretaceous sedimentary sequence, and extends northwest wards from the Moab-Spanish Valley salt anticline along the southwestern flank of a salt withdrawal syncline. The surface trace comprises a simple southern segment joined at branch-points to a series of fault splays in the north. Maximum surface throw occurs in the south where the fault is associated with both a footwall high and a hangingwall anticline. The fault trace is bordered by a damage zone, which includes a swarm of minor structures, that is most extensively developed within regions of structural complexity, for example around branch-points, fault bends, overlap zones and fault-related folds. The fault was active from the Triassic until at least the mid-Cretaceous. Distinctive types of veining, calcite cementation and iron oxide reduction are best developed adjacent to the...