The potential for groundwater contamination along basin margins in the arid west: Alluvial fans and lake features

Many towns of the arid west were built upon alluvial fans and upon sites underlain by Pleistocene lake deposits. The objective of this study was to assess the potential impact of these activities of man upon groundwater quality within these geological features. Emphasis was placed on shallow groundwater quality after it was determined that deep groundwater is rarely contaminated at such sites. A reconnaissance of Utah and Nevada was made and four sites underlain by alluvial fans (Willard, Manti, Elsinore, and Spring City) and four sites underlain by lake shore deposits (Hyde Park, Fielding, Providence and Richmond) were selected in Utah for more detailed geologic, hydrologic, and water quality studies. Samples for water quality analyses were taken from existing wells and springs where available. At Hyde Park a shallow, small diameter well was constructed. Three groundwater sampling wells were constructed on the Willard Creek fan. Sites were selected to represent various degrees and types of land use. It was concluded that septic effluents, agricultural wastes, and other sources of man-made contamination can be hazards to shallow groundwater quality in alluvial fans and lake shore sediments. Mercury was found in concentrations exceeding the EPA drinking water standards at a few of the sites, but its source was probably natural. Nitrates and phosphates usually were the observable indicators of shallow groundwater contamination at the sites investigated, while coliform bacteria evidently are not transported appreciable distances underground and made poor indicators. The conclusions reached in this report are believed to be applicable to other areas of the arid west where similar geologic features and basin margin sediments occur

The potential for groundwater contamination along basin margins in the arid west: Alluvial fans and lake features

Many towns of the arid west were built upon alluvial fans and upon sites underlain by Pleistocene lake deposits. The objective of this study was to assess the potential impact of these activities of man upon groundwater quality within these geological features. Emphasis was placed on shallow groundwater quality after it was determined that deep groundwater is rarely contaminated at such sites. A reconnaissance of Utah and Nevada was made and four sites underlain by alluvial fans (Willard, Manti, Elsinore, and Spring City) and four sites underlain by lake shore deposits (Hyde Park, Fielding, Providence and Richmond) were selected in Utah for more detailed geologic, hydrologic, and water quality studies. Samples for water quality analyses were taken from existing wells and springs where available. At Hyde Park a shallow, small diameter well was constructed. Three groundwater sampling wells were constructed on the Willard Creek fan. Sites were selected to represent various degrees and types of land use. It was concluded that septic effluents, agricultural wastes, and other sources of man-made contamination can be hazards to shallow groundwater quality in alluvial fans and lake shore sediments. Mercury was found in concentrations exceeding the EPA drinking water standards at a few of the sites, but its source was probably natural. Nitrates and phosphates usually were the observable indicators of shallow groundwater contamination at the sites investigated, while coliform bacteria evidently are not transported appreciable distances underground and made poor indicators. The conclusions reached in this report are believed to be applicable to other areas of the arid west where similar geologic features and basin margin sediments occur

Three-Dimensional Variation in Extensional Fault Shape and Basin Form: The Cache Valley Basin, Eastern Basin and Range Province, USA

Seismic reflection profiles, drill-hole data, and geologic maps delimit the form of normal faults and Tertiary sedimentary rocks in the southern half of the Cache Valley basin in northern Utah. Dips of faults and sedimentary rocks were estimated from time-migrated reflection profiles by using the stacking velocities for the data. At the southern end of the basin, the East Cache fault zone is listric; it shows 50°W dips near the surface and ≈20°W dips at depth. The fault zone has been the site of ≈5.6 km of net dip slip. Tertiary rocks dip 18°E–25°E and exhibit a rollover geometry above the fault zone. No faults are interpreted on the western side of the basin. In the central part of the basin in Utah, the East Cache fault is a single fault that dips at least 45°W near the surface and is the site of 4.5–6.4 km of net dip slip. Here, the basin is bounded to the west by the West Cache fault, which is the site of at least 1 km of net slip that increases northward to 2 km of net slip. Slip on the East Cache fault resulted in planar, east-dipping, older Tertiary rocks near the bottom of the basin. Younger Tertiary strata, with southwest, west, and northwest dips, reflect complex tilting due to slip on the West and East Cache faults. Anticlines in the Tertiary basin-fill deposits are present in the central part of the basin and may reflect changes in normal-fault geometry at depth. Northward, dip slip on the East Cache fault zone decreases to 2.5 km. The basin is broad, shallow, and filled with nearly flat lying Tertiary rocks. This area, near the north-south midpoint of the basin, is bounded by the West and East Cache faults, but slip on the West Cache fault appears to diminish northward. A north-trending reflection profile tied to both drill-hole data and the east-trending seismic profiles indicates that the basin is deeper in the southern end. The along-strike changes in fault geometry, the amount of fault-slip, the subsurface form of the basin-filling sedimentary rocks, and the form of the basin indicate a complex history of faulting and deposition during its formation. This study and other recent ones from the Basin and Range province indicate that such complexities may be typical of many Tertiary basins in the region

The Bear River\u27s Diversion and the Cutting of Oneida Narrows at ~55-50 ka and Relations to the Lake Bonneville Record

The Bear River’s course has shifted over Quaternary time, and its late Pleistocene integration into the Bonneville basin long has been recognized as a possible explanation for why Lake Bonneville was apparently larger than the preceding lakes in its basin, and the only one to overflow its topographic threshold. The middle-Pleistocene Bear River joined the Snake River to the north, likely via the Portneuf River drainage. Then an episode of volcanism in the Blackfoot-Gem Valley volcanic field ~100–50 ka diverted the Bear River southward into Gem Valley. Previous chronostratigraphic and isotopic work on the Main Canyon Formation in southern Gem Valley indicates internal-basin sedimentation during most of the Quaternary, with a possible brief incursion of the Bear River ~140 ka. New evidence confirms that the Bear River’s final diversion at ~55 ka led to its integration into the Bonneville basin by spill-over at a paleo-divide above present-day Oneida Narrows dam. This drove rapid incision of 200 m of bedrock in the canyon and excavation of southern Gem Valley in the subsequent millennia, before the rise of Lake Bonneville back flooded the area, as constrained by new optically stimulated luminescence dates above, within, and below the canyon. Bear River integration into the Bonneville basin early during marine isotope stage 3 seems to postdate the Cutler Dam lake cycle, although that penultimate pluvial lake is incompletely dated and understood. It is also possible the Bear River’s hydrologic addition relates to the recently recognized but poorly constrained Pilot Valley shoreline that predates the main Bonneville lake cycle. Regardless, the Bear River certainly contributed to the rise of Lake Bonneville, culminating in the Bonneville flood