title: Geology of the Southwestern Part of the Randolph Quadrangle, Utah-Wyoming
Creators: name: Hansen, Steven C.
Publisher: name: Utah State University
Year: 1964

description: General Statement
A detailed study of the southwestern part of the Randolph quadrangle was undertaken in view of the fact that Richardson (1941) mapped a large area of undifferentiated Ordovician rock. Therefore, the purposes of this investigation are: (1) to prepare a more detailed geologic map of the south­western part of the Randolph quadrangle (Plate 1), (2) to describe the struc­ture, stratigraphy, and geologic history of the area, and (3) to relate the geology to adjacent areas.
The elevation of the area mapped ranges from approximately 8, 910 to 6, 700 feet above sea level with the major part of the area above 8, 000 feet. This area forms part of the eastern ridge of the Bear River Range (Williams, 1948, p. 1, 125-1, 126). The southern boundary of the area extends east from the southwest corner of the Randolph quadrangle for a distance of about 4 miles. The eastern boundary extends northward about 11 miles and is parallel to the mountain front. The northern boundary is less well defined and is taken as the ridge separating Curtis Creek from the next canyon to the north. The western boundary extends south approximately 10 miles to the southwest corner of the Randolph quadrangle. The southwestern part of the Randolph quadrangle (Figure 1) covers approximately 56 square miles and lies approximately 60 per cent in Cache County and 40 per cent in Rich County. The major part of the area lies within the Cache National Forest.
The area mapped is generally accessible from mid-June to mid- September. A road is maintained along the length of the area by the U. S. Forest Service and is passable by automobile except during heavy rain- storms in the summer months.
Field Work
The field work was done during the summer of 1963. Formation con- tacts, attitudes, and faults were mapped in the field on aerial photographs of the approximate scale 1:20, 000. This information, concerning the south- western part of the Randolph quadrangle, was transferred to a base map constructed from the topographic map of the U. S. Geological Survey of the same area (1912 edition). The base map was enlarged to the scale 1:24, 000. Stratigraphic sections were measured with a 50-foot steel tape. A Brunton compass was used to measure attitudes and slope angles. Sample rock types were collected from each unit and compared with the rock-color chart (Goddard, 1951) to obtain standard color names. Fossils were collected and identified in the laboratory by the author.
Previous Investigations
The earlier geologic reports from the general area of the Randolph quadrangle are found in the Hayden Survey and the survey of the Fortieth Parallel supervised by King. Hayden (1871, p. 150-156), Peale (1877, p. 573-609), Hague (1877, p. 393-442), and Emmons (1877, p. 326-393) all commented upon the general area. Walcott (1908) studied the Cambrian rocks of the Bear River Range and defined eight formations. Veatch (1907) studied the area adjacent to the Randolph quadrangle in Wyoming. In the Randolph quadrangle, Richardson (1913) divided the Ordovician rocks into three formations, identified the Silurian rocks as a formation, defined one Mississippian formation, and later (1941) published a geologic map of the quadrangle. Mansfield's (1927) study of southeastern Idaho provided valu­able information concerning regional structure and stratigraphy. Williams (1948) mapped the Logan quadrangle which is adjacent to the area on the west. Specific studies (Ross, 1949, 1951; Maxey, 1941, 1958) have given more detailed information concerning Cambrian and Ordovician rocks of the area. A recent publication by Armstrong and Cressman (1963) is important in dating the uplift and thrust faulting in the ancestral Bear River Range. The Geologic Map of Utah (Stokes, 1961) followed the interpretaion of Richardson (1941), for the southwestern part of the Randolph quadrangle, except in the designation of the Wasatch formation which is shown as Knight conglomerate.