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Discovery of the Baldy toreva near urban areas along the southern Wasatch Range, Utah

Eric R. Meyer and Ron A. Harris
Discovery of the Baldy toreva near urban areas along the southern Wasatch Range, Utah
Rocky Mountain Geology (July 2020) 55 (1): 55-73


Structural and geomorphic studies, and lithostratigraphic and biostratigraphic mapping reveal that a giant toreva block (6.125 km3) slid off Mount Timpanogos toward what are now densely populated urban areas along the Wasatch Front of Utah. The block forms a prominent peak known as Big Baldy, which consists of steeply dipping and locally brecciated limestone and quartzarenite over nearly horizontal shale. Preferential erosion of this shale below overlying limestone and quartzarenite cliffs is most likely the cause of this particular landslide and potential future slides along the Wasatch Front. The low-angle contact at the base of the giant toreva block was initially mapped as a thrust, then as a low-angle normal fault. In both cases, these faults were inferred to have large amounts of displacement (900 meters), but no traces of such faults are found in adjacent canyons. The Baldy slide is associated with geomorphologic features, such as faceted spurs, landslide scarps, sackungen, and hummocky terrain. Limestone and quartzarenite beds in the block are back-rotated up to 80 degrees and are locally broken and brecciated. No evidence of hydro-fracturing is found in the breccia or of multiple brecciation episodes, which indicates surficial rather than deep-crustal processes and perhaps a single event of slip. We speculate based on structural reconstructions of the slide block, and interpolation of maximum downcutting rates on nearby streams, that the slide initiated between 700 and 500 ka. Discovery of the Baldy slide attests to the importance of recognizing the influence of surficial processes in mountain front development and demonstrate the ongoing geologic hazard of mass wasting to communities along the seismically active Wasatch Front and similar horst blocks.

ISSN: 1555-7332
EISSN: 1555-7340
Serial Title: Rocky Mountain Geology
Serial Volume: 55
Serial Issue: 1
Title: Discovery of the Baldy toreva near urban areas along the southern Wasatch Range, Utah
Affiliation: Brigham Young University, Department of Geological Sciences, Provo, UT, United States
Pages: 55-73
Published: 202007
Text Language: English
Publisher: University of Wyoming, Dept. of Geology and Geophysics, Laramie, WY, United States
References: 32
Accession Number: 2020-062989
Categories: Environmental geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus. incl. sect., strat. cols., geol. sketch maps
N40°22'60" - N40°22'60", W111°39'00" - W111°39'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, copyright, University of Wyoming. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202018
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