A TOURIST’S GUIDE TO THE GEOLOGY OF DIXIE NATIONAL FOREST, PINE VALLEY RANGER DISTRICT, SOUTHWEST UTAH

Southwest Utah is internationally famous for National Parks, such as Bryce Canyon and Zion, and each year millions of visitors come to view their geologic wonders. Less widely known is the geology of the nearby National Forests. Such is the case for Dixie National Forest, the largest Forest in Utah that occupies almost two million acres in portions of the Great Basin and Colorado Plateau. Three National Parks and two National Monuments are adjacent to the Forest and yet the scenic beauty preserved in them prevails over much of the Forest. Park visitors can often find abundant information about the geology that produced the scenery, but this information is usually lacking for visitors to a National Forest. In partnership with the National Forest Service, we are working on a pilot geology guide book for the Pine Valley Ranger District (PVRD) that we hope will be a model for other ranger districts.

In the PVRD, we have conducted (along with our students) new geologic studies, detailed geologic mapping, and radiometric dating that have greatly improved our understanding of the geologic, tectonic, and volcanic history of the area. The PVRD is host to one of natures most catastrophic geologic processes – volcanism. Magmatism during the Miocene (22-20 Ma.) produced several laccolithic intrusions (known as the Iron Axis) that domed the country rocks, resulting in catastrophic gravity sliding (large landslides) from their roofs, and volcanic ash flow eruptions. One of the largest, shallow emplacement laccoliths in the world (Pine Valley laccolith) caps the Pine Valley Mountains and is the prominent landmark of the PVRD. The geology guide will begin with a geologic history of the PVRD (e.g., a description of the major rock units, fossils, structures, laccoliths, etc.) followed by rod logs that takes the visitor on self-guided tours of geologic features that can be seen, or even walked to, from the main roads that cross the PVRD. Features of interest will be identified with annotated photographs, diagrams, and maps. Whether visitors are hiking in such places as the Pine Valley Mountain Wilderness, or simply gazing toward the mountains, a greater understanding of the PVRD’s geologic origins and history will enhance their appreciation of this wonderful scenery.