Speaker: Tom Bush, Pierce College Puyallup
Title: Stratigraphic and Structural Controls of Landscape Development, San Rafael Swell and Capitol Reef National Park Areas, South-Central Utah
Abstract: The San Rafael Swell and Capitol Reef National Park lie within the northwest portion of the Colorado Plateau, a vast roughly circular area centered on the four-corners of Utah, Colorado, New Mexico, and Arizona. This region attracts millions of visitors per year to the numerous public lands who marvel and the scenic landscapes, and for good reason. Rock formations in the plateau range in age from Proterozoic to Paleogene and record a long and complex geologic history. Although igneous and metamorphic rocks are pre-sent throughout the region, the landscapes are dominated by horizontal to somewhat deformed drab to colorful sedimentary rocks. The mostly horizontal, colorful strata in many areas are deeply carved, forming spectacular incised meanders, deep canyons, mesas, buttes, pinnacles, stone arches, and natural bridges. The spectacular landscapes have evolved over the last few million years during uplift of the Colorado Plateau and have been greatly influenced by stratigraphic and structural controls. More specifically, the interlayering of hard, resistant strata with soft, nonresistant formations, combined with joint, fault, and folding development from several distinct epi-sodes of deformation, have interacted to create the spectacular geomorphic features of the region.
The San Rafael Swell and Capitol Reef National Park areas of south-central Utah are dominated by regional-scale Laramide monoclonal folds that are cored by the resistant, large-scale, cross-bedded Triassic-Jurassic Navajo Sandstone. Softer, non-resistant strata strati-graphically above but structurally below the Navajo have eroded into strike-parallel valleys. Monocline uplift was accompanied by ante-cedent stream development across the Navajo, forming numerous slot canyons. Prominent sub-regional scale intersecting joint systems and faults have controlled running water pathways to also form slot canyons, as well as other scenic features such as natural bridges and arches.
South-east-directed view of the Waterpocket Fold, Capitol Reef National Park, from Strike Valley Overlook. This Laramide monocline stretches for nearly 100 mi (160 km) throughout south-central Utah and is the primary attraction of the park. The Triassic-Jurassic Navajo Sandstone forms the prominent east-facing dip surface on the right. T. Bush photo.
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