November 1, 2007

The Utah Geological Survey’s newest geologic map available to the public is the Spanish Fork quadrangle, which includes the cities of Payson, Salem, Spanish Fork, and Woodland Hills. The map identifies the rocks and sediments in this rapidly developing suburban area south of Provo in southeastern Utah Valley.

The geologic map can be used to derive the extent of geologic hazards, which include earthquake faults, landslides, and areas that may experience debris flows or debris floods at canyon mouths.

Sedimentary bedrock is exposed in the Wasatch Range. The map reveals new interpretations of bedrock stratigraphy and new details of bedrock deformation. The Wasatch fault zone separates the mountains from the valley, which is mostly covered by deposits of ancient Lake Bonneville.

The quadrangle includes parts of both the Provo and Nephi segments of the fault zone, both of which have the potential to generate large earthquakes up to magnitude 7.5. Also shown are two of the 13 large earthquake-induced landslides initiated by liquefaction along the Wasatch Front.

Smaller, more recent landslides have also occurred along unstable bluffs where the Spanish Fork cuts through a Lake Bonneville delta, causing economic losses. The distribution of surficial deposits, faults, and landslides shown on the map include some details not previously identified.

The Spanish Fork geologic map provides geologic data useful to city and county agencies, consulting geologists, and developers to address geologic hazards and resource issues such as the location of sand and gravel deposits and ground-water supplies. It will also be of interest to educators and others simply interested in learning about the fascinating geology of this area.

Mapping was jointly funded through a cooperative agreement between the Utah Geological Survey and the U.S. Geological Survey under the National Geologic Mapping Act.

Map 227 is available for $13.95 at the Natural Resources Map & Bookstore, located at 1594 West North Temple, Salt Lake City (801-537-3320 or 1-888-UTAHMAP; geostore@utah.gov).