Relict Patterned Ground, Bear River Range, North-Central Utah

Abstract

In the Bear River Range, northcentral Utah, thirty-nine widely distributed localities of three acres or larger show a morphology resembling periglacial patterned ground. In the total of 2,359 acres (954 ha) under study, aerial photographs reveal an arrangement of mounds by an alternately dark and light pattern. The mounds are evenly distributed on slopes of less than 10 percent and aligned in beaded stripes on slopes of more than 10 percent. The mounds range from 13 to 66 feet (4 to 20 m) across; the average mound diameter is about 40 feet (12 m). Only regolith is affected by the patterned morphology. The regolith in and between the mounds is derived from the same source, but the parent material varies among different localities. The location of patterned areas appears to be controlled by temperature and soil. Temperature is the primary factor. Slope aspect, potential insolation, average elevation, and amount of terrain affected correlate for different localities. These factors interact to produce approximately the same average annual, summer, and winter temperatures in patterned ground areas. The patterned ground is located where the controlling temperature coincides with the appropriate soil. Twenty-two areas of patterned ground are within the boundaries of a recent soil survey. An analysis of the soils suggests that patterned ground genesis is facilitated by soils with significant silt and clay components. Some soils affected by patterned morphology have large amounts of stones and cobbles. The evidence of erosion subsequent to formation indicates that patterned areas did not originate under present climatic conditions. During Pleistocene glacial periods, the calculated average annual temperature at these localities was 32°F. Differential frost heaving during the cooler periods of the Pleistocene is suggested as the process responsible for the creation of patterned morphology in the Bear River Range.