Geological Survey Bulletin 1229 Geology of the Circle Cliffs Area, Garfield and Kane Counties, Utah

LOCATION AND EXTENT OF AREA

The Circle Cliffs area, which is 50 miles southwest of Hanksville, Utah (fig. 1), consists of about 1,660 square miles of rugged canyon-and-mesa land. High cliffs form an oval rim around a central area deeply dissected by streams that head both in the central part and in the northern highlands and flow through gaps in the rimming cliffs. The Henry Mountains rise to the east; to the west are flat-topped Boulder Mountain and the Aquarius Plateau.

FIGURE 1.—Location of the Circle Cliffs area.

Access to the interior of the Circle Cliffs area by motor vehicle was limited to three unimproved roads during this study. The most traveled access road, which was built in 1948 by the U.S. Atomic Energy Commission to encourage uranium exploration, enters from the east through Burr Canyon at the location of the old Burr Trail. An old road, used by the Ohio Oil Co. in the early 1920's, enters from Hall Creek Valley via Muley Twist Canyon about 8 miles south of Burr Canyon. This road was impassable during the entire study because of lack of maintenance. Two more access roads were opened in the late 1940's. One enters the Circle Cliffs area from the northwest via the town of Boulder and Long Canyon; the other road, 20-30 miles to the south, forks off a road connecting the town of Escalante and "Hole in the Rock" on the Colorado River and enters the Circle Cliffs area via Harris Wash and Silver Falls Canyon. The Burr Trail and Long Canyon routes generally are passable during all seasons, but the Harris Wash-Silver Falls Canyon route must be used with caution, because in the fall it is frequently washed out by violent flash floods. Most of these access routes were maintained once a year by the Garfield County Highway Department. In the cliff-rimmed interior are many roads—some are in constant use, others are used only once or twice a year, but all are nearly always passable to vehicles having generous road clearance.

GEOGRAPHY AND PHYSIOGRAPHY

The Circle Cliffs area is part of the Canyon Lands section of the Colorado Plateaus physiographic province. Landforms most typical of the area are steep-walled canyons, hogback ridges along Hall and Sandy Creeks, flat windswept sand-covered benches surrounding the cliff-rimmed interior on all sides except the east, and flat-topped mesas in the interior and in the Henry Mountains basin. The maximum relief is about 4,800 feet. The lowest altitude, 4,000 feet, is at Hall Creek in the southeast part of the area, and the highest, 8,800 feet, is in the northwest corner of the map area on the slope of Boulder Mountain.

The climate is semiarid to arid. The average annual precipitation is about 7 inches and occurs as local thundershowers in late summer and as light snow and rain in winter. The first snow usually falls in the middle of November. In mid-December of 1954 as much as 6 inches of snow covered the ground, but generally the snow cover melts quickly and does not hamper travel in the area.

Vegetation consists dominantly of grasses and sage on the alluvium overlying the Kaibab Limestone, sage on the alluvium overlying the Moenkopi Formation, and juniper and piñon in areas of bedrock exposure and on windswept benches. The vegetation is similar to that growing in some parts of the Henry Mountains (Hunt and others, 1953, p. 27-35).

The area has no permanent population, and the land is used for cattle grazing by ranchers living in Boulder and Escalante. Uranium exploration and mining attracted a transient population ranging from about 5 to 50 people during 1954-58.

All drainage in the interior of the Circle Cliffs area is dendritic and almost perfectly adjusted to the bedding attitude of the traversed formations; thus, streams flow in a downdip direction. Canyons in the northwestern part of the area follow the principal northeast-trending joints instead of paralleling the bedding-dip direction and therefore trend 10-20° SW. of the dip direction. Streams draining the western part of the area discharge into the Escalante River, which flows along the southwest flank of the Circle Cliffs anticline to the Colorado River. Most streams in the eastern part of the area flow into Hall Creek, which follows an incised course southeastward along the Waterpocket fold to the Colorado River. The Escalante River is superimposed on the regional structure. The stream in Muley Twist Canyon and Hall Creek may both be superimposed, although they meander principally in the more easily eroded sediments along the strike and can be just as reasonably classified as subsequent streams.

Water flows all year in the southern reaches of Hall Creek. In the western and southwestern parts of the map area, the Escalante River and Deer Creek flow all year. Steep Creek, also in the western part of the area, flows intermittently. Additional water is supplied by springs that issue at the base of the Wingate Sandstone and flow as much as 40 gpm (gallons per minute), and springs at the base of the Shinarump Member of the Chinle Formation that flow 1-2 gpm.

PREVIOUS WORK

M. E. Thompson and his party of the Powell Survey traversed the west and north sides of the Circle Cliffs area in 1872. Gilbert (1874) traversed nearby regions in 1872 as a member of the Wheeler Survey. Thompson surveyed the area in 1874-75 (Gregory and Moore, 1931, p. 7-9). In 1873 Howell (1875) studied the stratigraphy between the Aquarius Plateau and the Henry Mountains, and in 1875-76 Gilbert (1877) mapped the Henry Mountains and parts of the Waterpocket fold. Gregory and Moore (1931) studied the geology of the Kaiparowits region in 1915-27. Moore mapped the geology of the Circle Cliffs area in considerable detail in 1921-22 as part of that study. Hunt remapped the Henry Mountains in 1935 and included parts of the Circle Cliffs area (Hunt and others, 1953). Steed (1954) published results of mapping and stratigraphic work in the Circle Cliffs area done in connection with the drilling of a second oil-test well near Wagon Box Mesa in 1954. Steed's work is published in a guidebook of the geology of the High Plateaus, which contains many papers regarding the geology of the region. Reports dealing primarily with stratigraphic problems in the Circle Cliffs and surrounding areas are those by Dake (1919, 1920), Moore (1922), Longwell, Miser, Moore, Bryan, and Paige (1923), Baker, Dane, and Reeside (1936), McKee (1938, 1954a, b), Craig and others (1955), Stewart (1957), and Stewart, Williams, Albee, and Raup (1959).

PURPOSE AND SCOPE

This report is based on work done on behalf of the U.S. Atomic Energy Commission to determine the mineral potential, primarily that of uranium, and to discover causes of localization of uranium ore in the Circle Cliffs area. Detailed geologic maps, prospect examinations, and analyses of prospect and outcrop rock samples were made to provide a sound geologic basis for the conclusions presented in this report. All prospects were examined, and some of the more promising ones were mapped in detail. The results of all the work are included in this report.

FIELD METHODS

Fieldwork was started in July 1954 and was completed in October 1957. Mapping parties were based at trailer camps in several parts of the area. When the area around a camp was mapped, generally about 60-100 square miles, the camp was moved to a new site. In this way areas of difficult access were rendered fairly accessible.

Travel in the Circle Cliffs is no longer as arduous as it was in 1872 when members of Powell's survey first examined the area. Roads suitable for pickup trucks and four-wheel-drive vehicles are abundant and occasionally are maintained. Some roads, or trails, are very rough, or are otherwise difficult for travel. Horses were used briefly in the southern part of the map area; Silver Falls, Big Bown, Little Bown, and the other benches in the southern part are accessible from only a few places, and at those places only on foot or horseback.

Topographic base maps (1953 edition) at a scale of 1 inch to 2,000 feet and a contour interval of 40 feet were used in field mapping. Field-inspection methods were used in most of the area to plot rock-unit features on the maps.

Geologic contacts in inaccessible areas were transferred to topographic maps from aerial photographs, mainly by the use of a Kale plotter. Contacts gained this way may be accurately mapped, but the consistency achieved was not always uniform. The southern part of the area, where formations of the Glen Canyon Group are the principal outcrop, was mapped photogrammetrically using the very accurate Kelsh plotter.

The base of the Wingate Sandstone cliff was located accurately by turning vertical angles on it from points of known altitude and position, using a transit, explorer's alidade, or a hand level. The approximate distance to the cliff was measured on the topographic map, and the altitude of the base was computed trigonometrically.

Stratigraphic sections were measured as time and circumstances permitted, some by U.S. Geological Survey personnel not directly associated with the Circle Cliffs project. In general, the bedding terminology used in the sections and in the rest of the report follows that suggested by McKee and Weir (1953).

ACKNOWLEDGMENTS

Geologists who assisted in mapping the area are Lorence C. Collins, in the summer of 1954; David A. Brew, in the fall of 1954 and the summer of 1955; Louis D. Carswell, in 1955-56; R. A. Cadigan for 2 months in 1956; and Glen A. Miller in 1956 and 1957. In 1957, Paul P. Orkild did most of the Kelsh plotting of the southern part of the area. Brew, Carswell, and Miller assisted in compiling field data in the winter months following the field seasons.

I was capably assisted in the fieldwork by John Ringle and John Avent, in 1954; Kent Kane and Richard Gilman, in 1955; Gilbert Thomas and Donald Schultz, in 1956; and Bill Long and Albert Specht, in 1957. Sam Pyeatt, John Moreland, Charles Sparks, Alva Newman, and William Bruggemeyer brought supplies and repeatedly moved the trailer camps. Max Behumin of Boulder, Utah, conducted a pack trip in the northwestern part of the area. The work was done under the supervision of A. L. Brokaw, D. G. Wyant, and L. C. Craig, for whose help and advice I am grateful.