GEOLOGIC HAZARDS AND ADVERSE CONSTRUCTION CONDITIONS IN THE ST. GEORGE – HURRICANE METROPOLITAN AREA, WASHINGTON COUNTY, UTAH

Southwestern Utah's mild climate and beautiful scenery combine to make the St. George area one of the Nation's fastest growing regions. As land well suited for development becomes increasingly scarce, urbanization has moved into less favorable areas where geologic hazards and adverse construction conditions are encountered. Where development takes place in less suitable areas, timely geologic information early in the planning and design process is critical to addressing geologic hazards and adverse construction conditions.

To provide that information, the Utah Geological Survey (UGS) has prepared a GIS-based map folio containing 14 1:24,000-scale geologic-hazard and adverse-construction-condition maps for the St. George - Hurricane metropolitan area (366 square miles). Each map has an accompanying text document that provides information on the nature and extent of the hazard/adverse condition in the study area. The maps are designed as an aid for general planning to indicate where detailed site-specific studies are required. A search application permits the maps to be queried by hazard/adverse condition type and location (township, range, and section; latitude and longitude; UTM; rectangular area; or tax identification number) and produces a map and report on the hazards/adverse conditions of interest.

Geologic-hazard maps in the folio include surface faulting, liquefaction, flooding, landslides, rock fall, and piping- and erosion-susceptible soils. Adverse-construction-condition maps include expansive soil and rock, collapsible soil, gypsiferous soil and rock, shallow bedrock, caliche, wind-blown sand, breccia pipes and paleokarst, and shallow ground water. The folio also includes a text document describing the earthquake ground-shaking hazard in the study area, but insufficient data were available to prepare a map.

The UGS will make the maps and search application available to Washington County and municipalities in the study area, and will assist them in preparing master plans and ordinances addressing geologic hazards and adverse construction conditions. The UGS will further assist the permit-approval process by reviewing geologic-hazards reports for proposed development, and for essential public facilities (police and fire stations, water tanks, schools).