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This GIS dataset is reproduced from: “Best, M.G., Grant, S.K., Hintze, L.F., Cleary, J.G., Hutsinpiller, A., and Saunders, D.M., 1987, Geologic map of the Indian Peak (southern Needle) Range, Utah: U.S. Geological Survey Miscellaneous Investigations Series Map I-1795, 1 plate, scale 1:50,000.” The map covers four standard 7.5' quadrangles in southwestern Utah: Atchison Creek, Pinto Spring, Steamboat Mountain SW, and Steamboat Mountain. The GIS dataset was completed by Laura Riley and Gerrit Gardner, students at Brigham Young University, and final GIS review and preparation for public release were completed by Zach Anderson, a geologist with the Utah Geological Survey.The UGS appreciates the volunteered time and effort of Brigham Young University students Laura Riley and Gerrit Gardner who produced the GIS data for this project under the guidance of Brigham Young University professor Eric Christiansen.The southern Needle Range area is in the Basin and Range Province of southwestern Utah and is dominated by north-south-trending mountain ranges and broad valleys. In the central part of the map, Lower Ordovician through Lower Pennsylvanian sedimentary rocks are exposed in four unique structural settings. From northwest to southeast, these Paleozoic sedimentary outcrops are: (1) a section of Ordovician and Devonian(?) rocks that are part of an intracaldera landslide, (2) a low-angle attenuation fault separating an incomplete section of Pennsylvanian Callville Formation from the Mississippian Monte Cristo Limestone, (3) steeply dipping and overturned Ordovician and Silurian rocks thrust over Mississippian and Pennsylvanian rocks, and (4) a section of Silurian and Devonian rocks that dip uniformly northwest. Thrust faulting is a result of contractional deformation that occurred during the Cretaceous Sevier orogeny. The attenuation faulting could have occurred during the Sevier orogeny or during orogenic relaxation immediately following the Sevier orogeny. Oligocene to Miocene volcanic, volcaniclastic and minor amounts of intrusive rocks unconformably overlie and intrude Paleozoic rocks. The entire map lies within the collapsed Indian Peak caldera. A portion of the topographic wall of the White Rock caldera, one of the sources of the numerous volcanic units within the area, is present in the south-central part of the map area. Northwest- to northeast-striking normal faults cut Paleozoic–Cenozoic rocks and are the result of the Tertiary Basin and Range extension. This dataset was produced as part of a UGS multi-decade effort to provide statewide intermediate-scale (approximately 1:50,000 to 1:100,000) GIS data to the public, federal to local government agencies, educational groups, exploration and development companies, and other map users. The GIS dataset reproduces the original source map as close as reasonably possible; however, some geologic decisions were made to resolve cartographic problems such as inconsistent faults and incomplete polygons. We changed some geologic line symbols to better match the UGS 2018 data model. While the map is considered a good representation of the geology of the map area, users should be aware that it was produced in 1987 and does not meet all modern cartographic, spatial control, or geologic standards. Line and point attributes and symbology were selected from current (2018) UGS schema and do not necessarily match the intent of the original map. Selected attributes most closely represent the general geologic interpretation depicted on the original map, but are not an exact match, as noted below. ContactsOriginal attributes are “Contact – Dashed where approximately located or inferred on cross sections.” These lines are now depicted as “Contact, well located.”Normal FaultsOriginal attribute is “High-angle fault – Dotted where concealed. Bar and ball on downthrown side.” These lines are now depicted as “Fault, normal, well located” or “Fault, normal, concealed.”General faultsLine types do not have a description in the explanation of the original map. These lines are now depicted as “Fault, unknown, well located” or “Fault, unknown, concealed.”Thrust FaultsOriginal attribute is “Thrust fault – Sawteeth on upper plate.” These lines are now depicted as “Fault, thrust, type1, well located;” where older rocks are faulted over younger rocks.Attenuation FaultsOriginal attribute is “Low-angle fault – Sawteeth on upper plate.” These lines are now depicted as “Fault, attenuation, exposed” where younger rocks are faulted over older rocks.FoliationOriginal attribute is “Strike and dip of compaction foliation in tuffs.” These points are now depicted as “Foliation, inclined, field measured” or “Foliation, horizontal.”Units – Descriptions/Names/AgesMap is not modified from original source map even in locations where newer interpretations may exist. |