What are those groovy rocks and how did they get that way?
by Carole McCalla

On a hike around Lake Blanche below Sundial Peak in Big Cottonwood Canyon, a group of hikers came across long, straight, parallel grooves on a smooth, polished rock surface. Recalling another location where they had seen similar features at the foot of the mountains north of downtown Salt Lake City, they wondered if these markings were formed in the same way. Indeed, what exactly are they and how were they formed?

Although the smooth, grooved surfaces at these two locations are similar, they were actually formed in very different ways.

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GEOLOGIC MAP OF THE CHARLESTON QUADRANGLE, WASATCH COUNTY, UTAH
Robert F. Biek and Mike Lowe

The Charleston quadrangle lies on the south edge of a structural and topographic saddle between the Wasatch Range and Uinta Mountains.  The quadrangle includes the southern part of Heber City and Heber Valley and the northern half of Round Valley, as well as parts of Deer Creek Reservoir and Wasatch Mountain State Park.  The quadrangle also straddles the north edge of the Charleston-Nebo thrust plate, and thus includes three distinct groups of rocks: (1) a nearly complete section of Pennsylvanian rocks of the Oquirrh Formation that comprises the Charleston thrust plate; (2) underlying, southeast-dipping Jurassic and Triassic strata below the Charleston thrust; and (3) Upper Proterozoic, Cambrian, and Mississippian strata that are exposed in a structurally complicated zone between the Charleston thrust and Deer Creek detachment faults.
A variety of late Tertiary and Quaternary deposits record the evolution of the present landscape.

This geologic map and report provide basic geologic information necessary to further evaluate geologic hazards and resources in the area, and to gain an understanding of the geology upon which this landscape developed.

CD (28 p., 2 pl., 1:24,000)

M-236………$14.95

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