| description:
|
This GIS dataset is reproduced from Patterson, C.G., Bromfield, C.S., Dubiel, R.F., Faulds, J.E., Larson, M.J., Milde, P.G., and Peterson, F., 1985, Geologic map of the Mt. Ellen-Blue Hills Wilderness Study Area and Bull Mountain study area, Garfield and Wayne Counties, Utah: U.S. Geological Survey Miscellaneous Field Studies Map MF-1756-B, 1 plate, scale 1:50,000. The map is compiled for use at 1:50,000 scale. The map depicts geologic formations, faults, bedding attitudes, folds, and other information, and is accompanied by explanatory information including correlation of map units, description of map units, structure discussion, references, and map symbols. This map covers the northern Henry Mountains and parts of flanking desert basins to the west, north, and east. It covers a large block in the western part of the Hanksville 30' x 60' quadrangle, and a small block in the eastern part of the Loa 30' x 60' quadrangle. It covers a large area just east of Capitol Reef National Park and includes Mt. Ellen, Table Mountain, Bull Mountain, South Caineville Mesa, Upper Blue Hills, Blue Valley, Blue Valley Benches, part of the Caineville Reef, the southern part of Red Desert, and a section of the Fremont River. State highway 24 passes through the northern part of the map area and highway 95 passes through the eastern part. Caineville Reef is an east-verging Laramide monoclinal fold. East of the reef, Upper Cretaceous strata are preserved in the synclinal Henry basin. Jurassic strata are exposed in the eastern and western parts of the map area. The Henry Mountains are the eroded remnants of Oligocene igneous laccoliths that intruded and steeply bowed up sedimentary rocks. Much of the landscape is stark redrock and blue-gray desert with exposed bedrock. Tributaries of the Fremont River are deeply incised into the terrain. Large pediments mantled with mostly igneous rocks extend from the Henry Mountains across much of the map area. Eolian sand and silt mantle some areas. This dataset was produced as part of a Utah Geological Survey (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 newer mapping in the area and the UGS 2019 data model. While the map is considered a good representation of the geology of the map area, users should be aware that it was released in 1985 and does not meet all modern cartographic, spatial control, or geologic standards.This map was compiled by the authors from published and unpublished sources. Some features were field verified, but it still should be considered a reconnaissance-type map. Comparison with current georectified orthophotographic imagery showed that spatial accuracy ranges from fairly accurate (generally within 10 to 20 meters) to very poor (some lines misplaced by more than 100 meters). The UGS did not attempt to improve the spatial fit of any features.Not all features on the original map precisely match options in the 2019 UGS geologic map schema as noted below. Line attributes and symbols were selected from current (2019) UGS schema and do not necessarily match the intent of the original map. Selected attributes most closely represent the general geologic interpretation depicted by the original map, but are not an exact match.ContactsA few contacts were slightly modified to close polygons, and a few superfluous contacts between polygons of the same unit were removed. Near Table Mountain a large polygon on the original map is labeled Qcl (revised to Qc) in one location and Qg (revised to Qag) in another; we either had to add a contact or change one label. We chose to change the Qag label to Qc as it seems more consistent with nearby mapping. Normal FaultsThese lines are now depicted as normal faults and unknown faults. Downthrown side is shown with bar and ball symbol.Anticlines and SynclinesThese lines are now depicted as approximately located or concealed where they are covered with Quaternary deposits.Units – Unit Symbols/NamesWhile we did not attempt to improve or change geologic map contacts or features, we did change some map unit labels to formation and member names preferred by most current workers in the area as explained in the GIS map metadata. New or modified terms include: Tarantula Mesa Sandstone (Mesaverde Formation on original map), Masuk Formation (Masuk Member of Mancos Shale on original map), Muley Canyon Sandstone (Emery Sandstone Member of Mancos Shale on original map), Naturita Formation (replaces Dakota Formation throughout Utah), Morrison Formation, Salt Wash and Tidwell Members (Tidwell Member not noted on original map); we also noted that the Navajo Sandstone map unit includes the Temple Cap Formation. The Temple Cap replaces the older term Page Sandstone in this area following Doelling, H.H., Sprinkel, D.A., Kowallis, B.J., and Kuehne, P.A., 2013, Temple Cap and Carmel Formations in the Henry Mountains Basin, Wayne and Garfield Counties, Utah, In Morris, T.H., and Ressetar, R., editors, The San Rafael Swell and Henry Mountains Basin—geologic centerpiece of Utah: Utah Geological Association Publication 42, p. 279–318, appendices. |