The St. George - Hurricane metropolitan area is one of the nation's fastest growing regions. As land well suited for development becomes scarce, urbanization has moved into less favorable areas where geologic hazards and geology related adverse construction conditions are a concern. This DVD includes a GIS search application that permits the maps to be queried by hazard and condition type and location.

This report presents the results of the Utah Quaternary Fault Parameters Working Group (hereafter referred to as the Working Group) review and evaluation of Utah’s Quaternary fault paleoseismic-trenching data. The purpose of the review was to (1) critically evaluate the accuracy and completeness of the paleoseismictrenching data, particularly regarding earthquake timing and displacement, (2) where the data permit, assign consensus, preferred recurrence-interval (RI) and vertical slip-rate (VSR) estimates with appropriate confidence limits to the faults/fault sections under review, and (3) identify critical gaps in the paleoseismic data and recommend where and what kinds of additional paleoseismic studies should be performed to ensure that Utah’s earthquake hazard is adequately documented and understood. It is important to note that, with the exception of the Great Salt Lake fault zone, the Working Group’s review was limited to faults/fault sections having paleoseismic-trenching data. Most Quaternary faults/fault sections in Utah have not been trenched, but many have RI and VSR estimates based on tectonic geomorphology or other non-trench-derived studies. Black and others compiled the RI and VSR data for Utah’s Quaternary faults, both those with and without trenches.

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.

The purpose of these guidelines for investigating geologic hazards and preparing engineering-geology reports, is to provide recommendations for appropriate, minimum investigative techniques, standards, and report content to ensure adequate geologic site characterization and geologic-hazard investigations to protect public safety and facilitate risk reduction. Such investigations provide important information on site geologic conditions that may affect or be affected by development, as well as the type and severity of geologic hazards at a site, and recommend solutions to mitigate the effects and the cost of the hazards, both at the time of construction and over the life of the development. The accompanying suggested approach to geologic-hazard ordinances and school-site investigation guidelines are intended as an aid for land-use planning and regulation by local Utah jurisdictions and school districts, respectively. Geologic hazards that are not accounted for in project planning and design often result in additional unforeseen construction and/or future maintenance costs, and possible injury or death.

On the afternoon of December 12, 2013, a large, joint-controlled block of the Shinarump Conglomerate Member of the Chinle Formation, with an estimated volume of almost 1400 cubic yards and weighing about 2700 tons, detached from the cliff face at the top of the Rockville Bench in Rockville, Utah. The block fell on to the steep Moenkopi Formation slope below the cliff, and shattered into numerous cobble- to very large boulder-sized fragments. The fragments moved rapidly downslope before striking and destroying a house, detached garage, and car at 368 West Main Street in Rockville. The two occupants in the house were killed. The purpose of this 20-page investigation wast to document the characteristics of the fatal rock fall; evaluate future rock-fall hazard at and near the site; and provide recommendations for homeowners, the Town of Rockville, and other officials to consider in managing rock-fall risk. Although the first fatal event, this rock fall is the sixth large rock fall within the Town of Rockville in the 35 years prior to December 12, 2013. Five of those events occurred within the past nine years, and at least three of those struck and damaged structures at the base of the Rockville Bench.

Moab Valley and the contiguous Spanish Valley comprise a popular residential and recreational area in east-central Utah. Geologic processes that created the rugged and scenic landscape of Moab-Spanish Valley are still active today and can be hazardous to property and life. To address development in areas with geologic hazards, the Utah Geological Survey (UGS) conducted a geologic-hazards investigation to provide information to Moab City and Grand County to help guide development and reduce losses from geologic hazards. This report includes maps of Moab Valley and the northern and central parts of Spanish Valley that provide information on geologic hazards to assist homeowners, planners, and developers in making informed decisions. The maps show areas where hazards may exist and where site-specific studies are advisable prior to development. The maps are for planning purposes only, and do not preclude the necessity for site investigations. Site-specific studies by qualified professionals (engineering geologists, geotechnical engineers, hydrologists) should evaluate hazards and, if necessary, recommend hazard-reduction measures. Because of the small scale of the maps, some hazard areas are not shown; hazard studies are therefore recommended for all critical facilities (for example, hospitals, schools, fire stations), including those outside the mapped hazard areas.

The Paleoseismology of Utah series makes the results of paleoseismic investigations in Utah available to geoscientists, engineers, planners, public officials, and the general public. These studies provide critical information regarding paleoearthquake parameters such as earthquake timing, recurrence, displacement, slip rate, fault geometry, and segmentation, which can be used to characterize potential seismic sources and evaluate the long-term seismic hazard of Utah's Quaternary faults. This Miscellaneous Publication presents the results of four individual investigations undertaken to acquire new geologic and paleoseismic data on the Washington fault zone in Utah and northernmost Arizona. (1) New 1:24,000 scale geologic mapping provides improved information on the location and length of young surface ruptures and the relative ages of displaced surficial deposits along the Washington fault zone. (2) A detailed paleoseismic trenching investigation of a scarp formed on a latest Quaternary alluvial fan near Dutchman Draw in Arizona provides new information on paleoearthquake timing, displacement, and recurrence necessary for evaluating the seismic hazard presented by the Fort Pearce section to the St. George metropolitan area. (3) Trace element and major oxide geochemical correlation and radiometric dating 40 Ar/ 39 Ar of mafic volcanic flows displaced across the fault zone in Arizona provide long-term (early to middle Quaternary) vertical sliprate estimates for the Fort Pearce and Sullivan Draw sections of the fault. (4) A geotechnical consultant's surface fault rupture hazard investigation conducted for the Utah Department of Transportation provides new information on fault locations, number of earthquakes, and displacement per earthquake on the central part of the Fort Pearce section