WSGS Projects
Geotourism
Information Pamphlet Focuses on Atlantic City-South Pass Area
The South Pass area’s complex geology, which includes abundant deposits of gold and other metals, prompted mineral exploration dating back to the 1860s and continuing to the present day. The WSGS is publishing an informational pamphlet that will describe the area’s geologic history, rock formations, and mineral deposits.
The rock record in the South Pass area covers over 3 billion years of geologic history. During this timeframe, the area experienced crustal accretion, volcanism, sedimentation, metamorphism, uplift, and erosion, which gave rise to the intricate geology and mineral deposits in the vicinity of South Pass.
This new information pamphlet will also give a glimpse into the history of mineral exploration and mining of gold and other metals in the South Pass area.
The Atlantic City-South Pass information pamphlet is part of a larger series of pamphlets featuring the geology of state parks across Wyoming. Other pamphlets in the series cover geology in Sinks Canyon, Bear River, Boysen, Buffalo Bill, Curt Gowdy, Edness K. Wilkins, Glendo, Guernsey, Hot Springs, Keyhole, and Seminoe state parks.
Large chevron fold with smaller parasitic folds in Archean metasedimentary rocks in the South Pass area. [Credit: WSGS]
Geologic Hazards
Mapping and Slip Rates of the East Gallatin-Reese Creek Fault System, Yellowstone
The WSGS and Montana Bureau of Mines and Geology are collaborating on a project in Yellowstone National Park, studying the 40-km-long East Gallatin-Reese Creek fault system (EGRCFS) that spans the Wyoming/Montana border. Geologists are mapping and measuring fault scarps—locations where past earthquakes have ruptured the ground surface—and dating deposits offset by fault scarps to better understand the geometry, extent, slip rates, and earthquake hazard of this fault system.
The motivation for this work came from the recognition of previously undocumented fault scarps along the EGRCFS from high-resolution lidar (light detection and ranging) topographic data published for Yellowstone National Park in 2021. These fault scarps cut across undated glacial sediments that were likely deposited at the end of the most recent ice age in the Rocky Mountains, known as the Pinedale glaciation, and indicate that the EGRCFS has experienced surface-rupturing earthquakes since that time.
The project involves geologists collecting samples from glacial deposits near the fault scarps for cosmogenic radionuclide exposure dating—a method that measures the time that a rock has been exposed to cosmic rays at the earth’s surface. The ages calculated from this exposure dating technique represent the time since these rocks were deposited and uncovered as glacial ice receded. Additionally, geologists are using lidar data to map the distribution and geometry of fault scarps along the EGRCFS and to calculate the vertical separation of surfaces across the fault scarps.
Knowing the exposure age of the deposits, and the vertical distance they are displaced across fault scarps, will provide important constraints on the faulting history of the EGRCFS, including the maximum age of the most recent surface-rupturing earthquake(s), how fast the fault is slipping, and whether the fault slip rates vary over time and along the length of the fault system. This information is fundamental to understanding the seismic hazard posed by the EGRCFS, and it will provide land managers and scientists with important data that can be used in making decisions to mitigate earthquake risk in the Yellowstone region.
Landslide Susceptibility Mapping in Southern Teton County
The WSGS is producing a deep-seated landslide susceptibility map for the southern half of Teton County in western Wyoming. Landslide susceptibility maps depict the relative likelihood of future landslide activity based on a location’s intrinsic geologic and topographic properties. For this study, WSGS geologists are analyzing rock strength and slope angle—two of the fundamental properties impacting slope stability. The map will pertain to deep-seated landslides—those that have a failure plane below the rooting depth of vegetation, and which typically involve bedrock. Examples of deep-seated landslides include slumps, translational landslides, and block slides.
This work is motivated by the need for detailed landslide susceptibility mapping in Teton County—an area that has experienced large, damaging landslides in both historic and recent times—and the availability of high-resolution input datasets. The presence in the study area of 1:24,000-scale geologic mapping and 1-meter-resolution lidar (light detection and ranging) digital elevation models will enable geologists to generate a susceptibility map at a higher resolution than the statewide landslide susceptibility map that the WSGS published in 2019.
Geologists are compiling geology map unit polygons from 58 published and unpublished geologic maps covering the study area. Map units will be classified into relative rock strength categories and intersected with slope-angle to produce the susceptibility raster. Susceptibility will then be compared to previously mapped landslides to validate the dataset.
The map is intended for use by government officials, land managers, businesses, and the public at-large. It will serve as a foundation for other landslide analyses useful to land managers and planners, such as landslide hazard maps that incorporate external triggering mechanisms, and landslide risk maps that display the intersection of landslide hazard with exposed assets and values.
Mapping
STATEMAP Projects
Geologists at the WSGS are working on a 1:100,000-scale bedrock map of the Medicine Bow 30' x 60' quadrangle in southeastern Wyoming. the project is through the U.S. National Cooperative Geologic Mapping Program (STATEMAP) managed by the U.S. Geological Survey.
U.S. Interstate Highway 80 (I-80) roughly bisects the quadrangle. In addition to the small towns of Arlington and Elk Mountain, which are along I-80, the quadrangle contains the towns of Hanna and Medicine Bow. Compiling a bedrock map to this scale for this area is partly motivated by ongoing WSGS projects on critical minerals in the Medicine Bow Mountains. The quadrangle exhibits a diverse range of geologic features, including the Cretaceous and Paleocene rocks that fill the Hanna Basin, Neoarchean and Paleoproterozoic metasedimentary and metavolcanic rocks in the nearby Medicine Bow Mountains, and post-Laramide Miocene rocks of the northern Saratoga Valley.
This map is scheduled to be published in 2026.
Another team of WSGS geologists are mapping a pair of 1:100,000-scale geologic maps, also through the STATEMAP program. The adjacent Red Desert Basin and Rawlins 30' x 60' quadrangles occupy nearly all of the Great Divide Basin, spanning an area between Rock Springs and Rawlins. Contained within both quadrangles are similar geologic units that share a deformation history related to the Laramide orogeny. With the exception of the Rawlins Uplift that hosts rocks that range from 2.6-billion-year-old granite and gneiss to less than 22-million-year-old sedimentary basin fill, most of the mapping area is blanketed by Cretaceous and Paleogene sedimentary strata deposited in shallow marine, nearshore, fluvial, and lacustrine environments.
These maps are key in the WSGS's effort to complete the mapping of Wyoming at the scale of 1:100,000, using modern digital methods following the Geologic Map Schema (GeMS) standards defined by the U.S. Geological Survey and used in most states. Digital maps at this scale are useful for regional geology and regional exploration for oil, gas, and minerals.
Both maps are scheduled to be published in 2025. The WSGS has participated in this and related federal mapping programs for nearly 30 years, and to date has produced more than 160 geologic maps at the 1:24,000 and 1:100,000 scales.
Three Surficial Maps of Quads in Central Wyoming Underway
The WSGS is completing 1:100,000-scale surficial maps for the Riverton, Thermopolis, and Carter Mountain quadrangles in central Wyoming. Carter Mountain, and portions of the Thermopolis and Riverton quadrangles, were mapped previously by James Case and Laura Hallberg. Staff geologists are working to fill in unmapped areas based on available photography and elevation models. Publication of the maps will continue the WSGS initiative to complete 1:100,000-scale surficial mapping across Wyoming.
Minerals
Geochemistry and Geochronology Reconnaissance of the Medicine Bow Mountains
The WSGS is conducting an analytically intensive geochemistry and geochronology reconnaissance project in the Medicine Bows Mountains. The Medicine Bows have high potential for critical mineral deposits vital to U.S. growth and stability. The area’s complex geology, including the juxtaposition of the Archean Wyoming Province with the accreted Colorado Province terranes along the Cheyenne Belt and associated shear zones, multiple episodes of mafic and felsic intrusions, thick packages of metasediments and metavolcanics, possible later metamorphic events, and Laramide uplift, suggest that diverse mineral systems exist within the Medicine Bows.
Historical mining in the area has confirmed the existence of economically viable gold, silver, copper, platinum group elements, and minor uranium and rare earth element deposits. Historical mining efforts also noted the existence of metals now considered critical, the presence of which has been confirmed by subsequent scientific studies. However, geochemical data for the region are not available in a comprehensive public database. Pre-existing data are inconsistent in methodology, elements analyzed, spatial coverage, and public availability.
This project will develop and conduct an exhaustive sampling program to target areas of known and unknown mineralization in shear-hosted veins; layered mafic-ultramafic intrusions and associated felsic intrusions along the Cheyenne Belt; felsic intrusions, pegmatites, and vein systems in the accreted Proterozoic terranes; Precambrian sulfide-rich metasediments and metavolcanics; radioactive paleoplacers; and REE- and uranium-rich pegmatites. The study area encompasses the entire Wyoming portion of the Medicine Bow Mountains—a Precambrian-core Laramide uplift.
This project will directly complement the airborne magnetic and radiometric survey that occurred in summer 2023 in the Medicine Bow and eastern Sierra Madre mountains. The goal is an integrated understanding of the geochemical, structural, petrological, and deformational processes that make up regional mineral systems; this will have the potential to aid mineral exploration efforts not only in the Medicine Bows, but also in areas with a similar geologic history, such as the Sierra Madre range to the west and elsewhere along the trend of the Cheyenne Belt.
Potential critical minerals in the project area: antimony, arsenic, barium, beryllium, bismuth, cobalt, chromium, fluorspar, gallium, germanium, hafnium, indium, magnesium, manganese, nickel, platinum group elements, scandium, tantalum, tellurium, tin, vanadium, zinc, and zirconium.
Medicine Bows - Geophysics
A high-resolution magnetic and radiometric survey, designed to optimize coverage of geologic features of greatest interest, was flown in summer 2023 in the Medicine Bow Mountains. The effort focused on the Lake Owen Complex, a Paleoproterozoic layered mafic intrusion with known PGE mineralization, and the surrounding area that includes the Cheyenne Belt, which marks the southern margin of the Wyoming Province. The survey includes magnetic and radiometric data collected from a helicopter along flight lines spaced no wider than 200 meters and a nominal terrain clearance of 60–120 m. The mineral systems of interest in the survey area include mafic magmatic, magmatic rare earth elements, placer, porphyry Cu-Mo-Au, and volcanogenic seafloor. Potential critical mineral commodities: antimony, arsenic, barium, beryllium, bismuth, cobalt, chromium, fluorspar, gallium, germanium, hafnium, indium, magnesium, manganese, platinum group elements, rare earth elements, scandium, tantalum, tellurium, tin, vanadium, zinc, and zirconium. There is additional potential for silver, gold, cadmium, copper, iron, lanthanum, lead, molybdenum, thorium, uranium, and yttrium.
The resulting data collected from this survey will be released to the public in the coming months.
Please see the U.S. Geological Survey news release for more information about this geophysical survey.
Sierra Madre-Elkhead Mountains-Medicine Bow Mountains—Geophysics
A high-resolution magnetic and radiometric survey is currently being acquired in the greater Sierra Madre-Elkhead Mountains-Medicine Bow Mountains region along the Wyoming-Colorado border. The survey is funded by the USGS Earth MRI and is designed to meet complementary needs related to geologic mapping and mineral resource research. The survey design is coordinated with the WSGS, Colorado Geological Survey, and staff from the National Cooperative Geologic Mapping Program to optimize coverage of geologic features of greatest interest. The survey is also designed to adjoin and augment the Medicine Bow Mountains airborne magnetic and radiometric survey.
The effort is focused on the Cheyenne Belt corridor along the southern margin of the Archean Wyoming Province, a region that contains several known and suspected mineral systems of high interest for their critical mineral potential. There has been abundant past and current exploration and mining, although exploration efforts are hampered by a lack of high-quality geophysical data. Several fundamental questions on the region's structure and Paleoproterozoic tectonomagmatic evolution are also unresolved.
The airborne survey data are further expected to aid mapping of suspected Quaternary faults and elements of the geology important to groundwater resources in the Saratoga Valley. The planned survey includes magnetic and radiometric data collected from a helicopter along flight lines spaced 200 meters and a nominal terrain clearance of 100 m. Parts of the survey area may be suitable for a fixed-wing aircraft.
The mineral systems of interest in the survey area include Climax-type, mafic magmatic, magmatic rare earth elements, placer, porphyry copper-molybdenum-gold, and volcanogenic seafloor. Potential critical mineral commodities: antimony, arsenic, beryllium, bismuth, cobalt, chromium, fluorspar, hafnium, gallium, germanium, indium, magnesium, manganese, nickel, niobium, platinum group elements, rare earth elements, scandium, tantalum, tellurium, tin, vanadium, and zirconium. There is additional potential for cadmium, copper, gold, iron, molybdenum, lead, selenium, silver, vermiculite, and uranium.
Western Phosphate Field—Geochemistry
The WSGS is part of a four-state cooperative effort, administered by the Idaho Geological Survey and funded by the USGS Earth MRI program, to evaluate the enrichment of critical minerals in the Permian Phosphoria Formation. Exposures of this formation occur across 350,000 square kilometers in Idaho, Utah, Wyoming, and Montana, and it is one of the largest commercial resources of phosphate rock in the world. Mining of the Phosphoria Formation in this region, referred to as the Western Phosphate Field, has provided phosphorus for the fertilizer industry since the early 1900s.
The Phosphoria Formation formed within a marine chemocline system, and includes a succession of black organic-rich mudstones, siltstones, phosphorites, carbonates, and cherts deposited 265 million years ago on the western margin of North America. The richest phosphate deposits are in the Meade Peak and Retort members, which both display considerable lithologic and stratigraphic variability. Previous studies have shown that elevated levels of rare earth elements and other critical minerals are concentrated within phosphorites and black shales in these two members.
The project centers on collecting new geological and geochemical data primarily from the Meade Peak and Retort members. Data are being acquired along measured stratigraphic sections in the context of a basinwide framework and at locations considered strategic from a mineral resource or scientific standpoint (for example: suitable outcrops, mine exposures, and archived drill core). The objective is to construct geologic models that assess and delineate the critical mineral resource potential of the Western Phosphate Field in order to provide an enhanced understanding of marine chemocline mineral systems. Potential critical minerals in project area: chromium, fluorine, rare earth elements, and vanadium.
South Pass and Granite Mountains—Geophysics
A high-resolution magnetic and radiometric survey in the greater South Pass-Granite Mountains region in central Wyoming is now complete. The survey was designed to optimize coverage of geologic features of greatest interest and meet complementary needs related to geologic mapping, mineral resource research, and mapping of Quaternary faults.
The effort focuses on the areas encompassing and surrounding the Oregon Trail Structural Belt, which may represent the largely obscured boundary between the Beartooth-Bighorn magmatic zone and the southern accreted terranes. This region contains several known and suspected mineral systems of high interest for their critical mineral potential, and has been the subject of abundant past and current exploration and mining.
The area covers the South Pass-Atlantic City region, Rattlesnake Hills, Granite Mountains, and the Seminoe-Ferris mountains. Additionally, the airborne survey data are expected to aid in mapping and investigations along the North and South Granite Mountains faults, the Continental Fault, and other suspected Quaternary faults. The survey includes magnetic and radiometric data collected from a helicopter along flight lines spaced 200 meters and a nominal terrain clearance of 100 meters.
The mineral systems of interest in the survey area include alkalic porphyry, mafic magmatic, magmatic REE, metamorphic graphite, meteoric convection, orogenic gold, porphyry Cu-Mo-Au, and volcanogenic seafloor. Potential critical mineral commodities: aluminum, antimony, arsenic, barium, beryllium, bismuth, cobalt, chromium, fluorspar, gallium, germanium, graphite, hafnium, indium, manganese, niobium, nickel, platinum group elements, rare earth elements, scandium, tantalum, tin, tungsten, vanadium, zinc, and zirconium. There is additional potential for cadmium, copper, gold, iron, lead, mercury, molybdenum, phosphorus, selenium, silver, thorium, and yttrium.
The resulting data collected from this survey was released in February 2024.
Please see the U.S. Geological Survey news release for more information about this geophysical survey.
Water
Tensleep Sandstone Aquifer
WSGS hydrology staff are completing a compilation project focused on the Tensleep Sandstone aquifer—an important aquifer in Wyoming.
“We have compiled groundwater quality, porosity, permeability, water drive, bottom hole temperatures, and sample water temperatures. We have seen some interesting patterns, and we will share them in an upcoming report,” says WSGS hydrogeologist, Kurt Hinaman.
The Tensleep and its equivalent geologic formations occur statewide east of the Overthrust Belt and the Absaroka Range. They supply drinking and stock water along many basin margins in Wyoming. Additionally, the Tensleep is a reservoir for oil, and is one of the target aquifers in deep basins for the sequestration of carbon dioxide.
Madison Limestone Aquifer
WSGS hydrology staff have embarked on a compilation project focused on the Madison Limestone aquifer—an important aquifer in Wyoming.
“We are using our earlier work on the Tensleep aquifer as a template. We are compiling many of the same parameters as with our pathfinding Tensleep work,” says WSGS hydrogeologist, Kurt Hinaman.
The Madison and its equivalent geologic formations occur statewide east of the Overthrust Belt and the Absaroka Range. They supply drinking and stock water along many basin margins in Wyoming. Additionally, the Madison is a reservoir for oil, and is one of the target aquifers in deep basins for the sequestration of carbon dioxide. Data about the Madison aquifer that will be covered in the publication include groundwater quality, porosity, permeability, surface recharge, water drive, bottom hole temperatures, and sample water temperatures.