Reconnaissance of the Little Valley landslide, Draper, Utah: Evidence for possible Late Holocene, earthquake-induced reactivation of a large, pre-existing landslide (OFR-520)

By: F. X. Ashland

Using geomorphic analysis, and radiocarbon ages from a consultant’s landslide investigation, this publication outlines a partial movement history for the Little Valley landslide in Draper, Utah, and an approach for recognizing earthquake-induced reactivation in preexisting slides in the Wasatch Front. The landslide is a large, prehistoric, dormant debris slide, parts of which are undergoing or proposed for residential development. The presence of rotated blocks with deformed and faulted latest Pleistocene-Holocene sag pond sediments and local troughs with latest Pleistocene-Holocene alluvium allowed dating of movement episodes and periods of dormancy.

The age of graben-fill sediments in the head of the landslide indicates that the slide had formed prior to the onset of Late Pleistocene Lake Bonneville. A latest Pleistocene movement episode is suggested based on the preservation of the foot of the landslide that extends about 360 feet downslope of the Bonneville shoreline and overridden shoreline sediments at the toe of the slide. The youngest dated movement episode (4700 cal yr. B.P.) is based on the age of the base of a colluvial wedge associated with an antithetic, sag-pond-bounding fault that offsets organic silt in the head of the landslide. This movement overlaps in time with surface-faulting event W on the Salt Lake City segment of the Wasatch fault zone. The movement occurred during a dry period of the Holocene, supporting a possible seismic origin.

Other Information:
Published: 2008
Pages: 17 p.
Location: Salt Lake County
Media Type: Paper Publication