The Gilbert Episode in The Great Salt Lake Basin, Utah

By: Charles G. Oviatt

This 20-page report summarizes observations of sediments and shorelines of the Gilbert episode in the Bonneville basin of northwestern Utah. Lake Bonneville dropped to altitudes similar to those of modern Great Salt Lake by 13,000 years ago, remained low for about 1400 years, then rapidly rose about 50 ft (15 m) during the Gilbert episode (about 11,600 years ago). The Gilbert lake was probably less extensive than shown by previous mapping of the Gilbert shoreline. The lake reached altitudes of 4250-4255 ft (1295-1297 m), and its shoreline, which is not well defined anywhere in the basin, was probably not deformed by residual isostatic rebound associated with removal of the Lake Bonneville water load. Holocene Great Salt Lake has not risen as high as the Gilbert-episode lake.

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Investigation of Land Subsidence and Earth Fissures in Cedar Valley, Iron County, Utah

By: Tyler Knudsen, Paul Inkenbrandt, William Lund, Mike Lowe, and Steve Bowman

This 116-page report presents the results of an investigation by the Utah Geological Survey of land subsidence and earth fissures in Cedar Valley, Iron County, Utah. Basin-fill sediments of the Cedar Valley Aquifer contain a high percentage of fine-grained material susceptible to compaction upon dewatering. Groundwater discharge in excess of recharge (groundwater mining) has lowered the potentiometric surface in Cedar Valley as much as 114 feet since 1939. Groundwater mining has caused permanent compaction of fine-grained sediments of the Cedar Valley aquifer, which has caused the land surface to subside, and a minimum of 8.3 miles of earth fissures to form. Recently acquired interferometric synthetic aperture radar imagery shows that land subsidence has affected approximately 100 mi² in Cedar Valley, but a lack of accurate historical benchmark elevation data over much of the valley prevents its detailed quantification. Continued groundwater mining and resultant subsidence will likely cause existing fissures to lengthen and new fissures to form which may eventually impact developed areas in Cedar Valley. This report also includes possible aquifer management options to help mitigate subsidence and fissure formation, and recommended guidelines for conducting subsidence-related hazard investigations prior to development.

Although this product represents the work of professional scientists, the Utah Department of Natural Resources, Utah Geological Survey, makes no warranty, expressed or implied, regarding its suitability for a particular use. The Utah department of Natural Resources, Utah Geological Survey, shall not be liable under any circumstances for any direct, indirect, special, incidental, or consequential damages with respect to claims by users of this product.

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Interim Geologic Map of the Enoch Quadrangle, Iron County, Utah

By: Tyler R. Knudsen

The Enoch quadrangle, in eastern Iron County, Utah, includes the northeastern part of Cedar Valley and parts of the adjacent Red Hills. The Red Hills-structurally consisting of an elevated, fault-bounded horst block-expose the upper parts of the Tertiary Claron Formation as well as a chaotic mass of Miocene and Oligocene volcanic rocks that may be part of the Markagunt Megabreccia that is widely exposed on the central and northern Markagunt Plateau to the east. Basaltic andesite flows cover large parts of the North Hills in the northeastern part of the quadrangle. Earth fissures related to groundwater overdraft of the Cedar Valley aquifer and resultant land subsidence have formed along parts of the eastern and western margins of the Enoch graben.

This CD contains two plates-a geologic map at 1:24,000 scale and an explanation plate-and a 12-page booklet, all in PDF Format. The latest version of Adobe Reader is required to view the PDF files.

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Interim Geologic Map of the Cedar City NW Quadrangle, Iron County, Utah

By: Tyler R. Knudsen and Robert F. Biek

The Cedar City NW quadrangle includes the southwestern part of Cedar Valley and parts of the adjacent Eightmile Hills and Granite Mountain in Iron County, Utah. Exposed strata range from the Jurassic Temple Cap Formation to Oligocene-age quartz monzonite of the Granite Mountain laccolith. Emplacement of the Granite Mountain and Three Peaks laccoliths was controlled by the east-verging Sevier-age Iron Springs Gap thrust fault. Replacement manetite-hematite ore bodies in the Co-op Creek Limestone Member exist locally along the margins of the laccoliths and have made the Iron Springs mining district the largest iron-producing district in the western U.S. In the Eightmile Hills, regional ash-flow tuffs are locally involved in a large gravity slide shed off the Granite Mountain laccolith. Earth fissures related to groundwater overdraft of the Cedar Valley aquifer and resultant land subsidence have formed north and west of Quichapa Lake.

This CD contains two pates-a geologic map at 1:24,000 scale and an explanation plate-and a 18-page booklet, all in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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Interim Geologic Map of the Cedar City 7.5-Minute Quadrangle, Iron County, Utah

By: Tyler R. Knudsen

The Cedar City 7.5′ quadrangle is roughly centered on the rapidly-growing community of Cedar City in Iron County, Utah. It straddles the boundary between the Basin and Range and Colorado Plateau physiographic provinces, which at the latitude of the quadrangle, is defined by the north-south-trending Hurricane fault. The eastern half of the quadrangle encroaches on the western margin of the Markagunt Plateau (Colorado Plateau). Rocks there are mostly Mesozoic in age, and have been moderately to highly deformed by Sevier-age thrusting and folding and by later basin-and-range-style normal faulting. The western half of the quadrangle lies in Cedar Valley, a typical Basin and Range basin filled with hundreds to thousands of feet of unconsolidated basin-fill sediments and basaltic lava flows.

This CD contains two plates-a geologic map at 1:24,000 scale and an explanation plate-and a 20-page booklet, all in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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Geologic Map of The Vernon NE Quadrangle, Tooele County, Utah

By: Stefan M. Kirby

This map represents the geology of the Vernon NE quadrangle at 1:24,000 scale. The Vernon NE quadrangle covers a part of the floor of Rush Valley northeast of the Vernon Hills in southeastern Tooele County. Unconsolidated surficial deposits of Holocene to lower Pleistocene? age cover nearly the entire quadrangle. These deposits include various alluvial fan and channel sediments, and lacustrine units deposited during both the transgression and regression of Lake Bonneville. The Salt Lake Formation is exposed in the western half of the quadrangle as a series of topographically low outcrops partially overlain and surrounded by unconsolidated deposits. The exposed thickness of the Salt Lake Formation is up to 2850 feet (870m).

This CD contains geographic information system (GIS) files in ESRI file geodatabase and shapefile formats. Two plates, a geologic map at 1:24,000 scale and an explanation plate, and a 6-page booklet are also included in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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Geologic Map of The Faust Quadrangle, Tooele County, Utah

By: Stefan M. Kirby

This map represents the geology of the Faust quadrangle at 1:24,000 scale. The Faust quadrangle covers part of Rush Valley and includes the southeastern part of the Onaqui Mountains, the northernmost Vernon Hills and adjoining parts of the valley floor in southeastern Tooele County, Utah. Most of the Faust quadrangle is covered by unconsolidated deposits of Holocene to Pleistocene age. These deposits include various alluvial fan and channel deposits, and lacustrine units deposited during the maximum transgression of Lake Bonneville. At least two prominent systems of normal faults along the flank of the Onaqui Mountains and near the Vernon Hills cut unconsolidated deposits within the quadrangle. Sedimentary rocks exposed in the quadrangle include folded Pennsylvanian bedrock of the Oquirrh Group consolidated Tertiary basin fill of the Salt Lake Formation.

This DVD contains geographic information system (GIS) files in ESRI file geodatabase and shapefile formats. Two plates, a geologic map at 1:24,000 scale and an explanation plate, and an 8-page booklet are also included in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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Geologic Map of The Saint John Quadrangle, Tooele County, Utah

By: Stefan M. Kirby

This map represents the geology of the Saint John quadrangle at 1:24,000 scale. The Saint John quadrangle, in southeastern Tooele County, Utah, covers a part of the floor of Rush Valley. Unconsolidated surficial deposits of Holocene to Pleistocene age cover nearly the entire quadrangle. These deposits include various alluvial fan and channel sediments, and lacustrine units deposited during both the transgression and regression of Lake Bonneville. Normal faults cut unconsolidated deposits in the western half and northeast corner of the quadrangle. In the northeast corner of the quadrangle, conjugate normal faults form a prominent horst and a series of west-facing scarps in late Pleistocene mixed alluvial and lacustrine deposits. Bedrock includes Pennsylvanian-age Oquirrh Group sedimentary rocks exposed in the southwest corner of the quadrangle, which consists of interbedded marine limestone and sandstone. Consolidated Tertiary fine-grained lacustrine basin fill of the Salt Lake Formation is exposed just north of the community of Saint John.

This CD contains geographic information system (GIS) files in ESRI file geodatabase and shapefile formats. Two plates, a geologic map at 1:24,000 scale and an explanation plate, and an 8-page booklet are also included in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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Regional Groundwater Flow and Water Quality in The Virgin River Basin and Surrounding Areas, Utah and Surrounding Areas, Utah and Arizona

By: Paul Inkenbrandt, Kevin Thomas, and J. Lucy Jordan

In this 46-page report, we characterized the deep aquifer system and its connections to the overlying aquifers in the area of the Hurricane fault in Washington County by examining well logs, creating regional potentiometric-surface maps, compiling groundwater quality data, conducting gravity surveys, examining remote sensing data for surface lineaments, and determining areas for potential monitoring wells. Results of the study were: (1) R and C aquifer groundwater depths are > 500 feet in the I-15 corridor area, (2) a groundwater divide likely exists south of the Utah-Arizona state line, (3) groundwater flow follows open fracture systems, (4) fracture conductivity is highest near the fault, (5) dissolution of evaporites increase groundwater TDS, and (6) a well should be drilled into the Hurricane fault near Pintura.

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The Pony Express Basaltic Ash: A Stratigraphic Marker In Lake Bonneville

By: Charles G. Oviatt and Barbara P. Nash

The Pony Express basaltic ash is locally a useful stratigraphic marker in Lake Bonneville sediments in west-central Utah. The ash was erupted from a vent in the Sevier Desert basin soon after Lake Bonneville had transgressed high enough to flood into the basin about 24,000 years ago. The ash is found at or near the base of the Bonneville marl below altitudes of 1400m (4600 ft) in part of the Sevier Desert basin and the southernmost part of the Great Salt Lake basin. The chemical composition of the ash is similar to that of other basalts in the Sevier Desert. Possible source vents are in the Pahvant Butte area or a maar near Smelter Knolls.

This CD contains a 10-page report in PDF format. The latest version of Adobe Reader is required to view the PDF files.

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