Geologic Road, Trail, and Lake Guides to 's Parks and Monuments 2000 Utah Geological Association Publication 29 P.B. Anderson and D.A. Sprinkel, editors

GEOLOGICAL ROAD GUIDE TO QUAIL CREEK STATE PARK, WASHINGTON COUNTY, UTAH Robert F. Biek Utah Geological Survey Salt Lake City, Utah

INTRODUCTION

Quail Creek State Park lies astride one of the most remarkable geologic features in southwestern Utah. The park is cradled in the eroded core of the Virgin anticline, a generally symmetrical fold formed during the middle Cretaceous to early Tertiary Sevier orogeny. The flanks of the fold provide spectacular exposures of parts of the late Early Triassic Moenkopi Formation and overlying Late Triassic Chinle Formation, and Quaternary boulder deposits at the northwest end of the reservoir provide a glimpse into the rock types of the distant Pine Valley Mountains. Quail Creek State Park is also the site of a major engineering catastrophe that occurred on January 1, 1989, when the Quail Creek south dike suddenly failed.

Quail Creek State Park is a mecca for fishing, boating, and swimming, but despite its truly classic geologic setting, there are currently no developed trails in the park. Still, the views from the park road alone provide a remarkable glimpse into the heart of the Virgin anticline and the geology of southwestern Utah (figure 1) (Biek, 1999). A geologic map and stratigraphic column for the park are shown in figures 2 and 3.

MILEAGE DESCRIPTION INTERVAL/CUMULATIVE

0 0 BEGIN road log at the junction of Utah 9 and 318 near the axis of the Virgin anticline. PROCEED NORTH ON UTAH 318 to Quail Creek State Park. The road to the park heads north over the Shnabkaib Member of the Moenkopi Formation. Note microbiotic soils developed on weathered gypsiferous Shnabkaib strata.

1.0 1.0 TURN RIGHT into parking area at the Quail Creek south dike. STOP 1. GENERAL GEOLOGY OF QUAIL CREEK STATE PARK AND CATASTROPHIC FAILURE OF THE QUAIL CREEK SOUTH DIKE.

1 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah

Figure 1. Topographic map showing Quail Creek State Park and the surrounding area, with route for this road log.

2 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29 ated ated photograph shows the view looking northeast toward Quail Creek Reservoir. Creek Quail toward northeast looking the view shows photograph Figure 2. Geologic map and cross section of the Quail Creek State Park area in Washington County, Utah. The accompanying annot accompanying The Utah. County, Washington in area State Park section of the Quail Creek cross and map 2. Geologic Figure

3 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah

Figure 3. Rocks present in Quail Creek State Park and surrounding area. Only those intervals highlighted in color are present in the park; enclosing rock units are found in nearby areas. 4 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29

This parking area straddles the axis of the Virgin anticline, a 30-mile (48-km) long, northeast-trending, generally symmetrical fold formed during the Sevier orogeny. In fact, Quail Creek State Park owes its existence to the Virgin anticline, which, with two small dams, forms a natural catchment for offline storage of water (figures 4 and 5). The anticline is made all the more visible by the resistant Shinarump Conglomerate Member of the Chinle Formation, which forms a prominent carapace along the central portion of the fold (figure 6). The Virgin anticline is truly a classic geologic feature, and because it is so clearly expressed, and only sparsely covered by vegetation and Quaternary deposits, it is visited by geology field camp teachers and students from around the country.

Figure 4. Aerial view to the north of the Virgin anticline and Quail Creek Reservoir. Utah Highway 9 cuts across the Virgin anticline at the bottom of the photograph. The snow-covered Pine Valley Mountains are to the west and the Kolob Canyons section of is to the east. Photo by Janice Higgins, Utah Geological Survey.

The Virgin anticline has three similar structural domes along its length. From south to north these are Bloomington dome, Washington Dome, and Harrisburg Dome, each of which is cored by the Harrisburg Member of the Kaibab Formation (late Early Permian) (figure 7). A number of west-dipping thrust faults repeat Triassic and Jurassic strata on the northwest flank of the anticline, near Leeds (Proctor, 1953; Proctor and Brimhall, 1986; Biek, 1997, 1998). The northeast-plunging nose of the Virgin anticline is complicated by numerous normal faults and subsidiary folds, which likely formed during the Sevier orogeny (Biek, 1998). One such down-to-the-east normal fault that displaces Shinarump strata is visible at the crest of the anticline at the north end of the reservoir (figure 6). An example of thrust fault deformation is described below at mile 1.5.

At 12:30 a.m. on January 1, 1989, the Quail Creek south dike failed catastrophically, unleashing a torrent of water and causing millions of dollars of damage. Fortunately, the downstream area was evacuated in time to avoid fatalities. Approximately 25,000 acre-feet (30,492,000 m3) of water - more than half the reservoir's capacity - flowed through a breach in the dike over a 12-hour period (figure 8).

5 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah appearance of the Shnabkaib Member; the the Member; Shnabkaib the of appearance @ bacon-striped A

near the base of the upper red member; and the cliff-forming Shinarump Conglomerate. Conglomerate. Shinarump cliff-forming and the member; red upper of the base the near @ Purgatory sandstone, Purgatory A yellowish-brown sandstone, locally known as the the as known locally sandstone, yellowish-brown Note also the small normal fault and deeply dissected landslide at the north end of the reservoir. the of end north the at landslide dissected deeply and fault normal small the also Note Figure 5. View northeast to Quail Creek State Park, with Utah Highway 9 in the foreground. Note the Note in the foreground. 9 Utah Highway with State Park, Creek to Quail northeast 5. View Figure 6 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29

Shinarump Conglomerate

landslide upper red member

Shnabkaib Member

Figure 6. View northeast from the top of the Shinarump cliff, immediately west of the Quail Creek south dam parking area. Note how the Shinarump Conglomerate forms a resistant cap over the more easily eroded Moenkopi Formation. Note also the old, deeply eroded landslide just north of Quail Creek Reservoir. The base of the landslide is in Shnabkaib strata, which are comparatively weak and unstable.

Figure 7. View to the southwest along the axis of the Virgin anticline. Harrisburg Dome and Washington Dome form the low hills in the middle distance; the east limb of the anticline is also clearly visible.

7 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah

Figure 8. Quail Creek south dike, shortly after its catastrophic failure on January 1, 1989. Note how flood waters scoured the bedrock clean of loose, overlying sediments just below the dike. Photo courtesy of Ben Everitt, Utah Division of Water Resources.

The original Quail Creek south dike was a 78-foot (24-m) high, 2,000-foot (610- m) long earthen dam constructed in 1984. The dam was poorly designed and seepage under the dam occurred immediately after filling the reservoir. Seepage and sinkhole development increased in succeeding years despite efforts to seal the leaks (O'Neill and Gourley, 1991; Gourley, 1992). Seepage water probably passed under the dike, or at the dike-foundation contact, and began to erode the dike materials and in-situ soils. Ultimately, seepage and erosion of the dike and foundation materials continued and accelerated until caving occurred on a developing opening in the dike. Frantic last-minute efforts to stem the seepage were unsuccessful and the dike finally breached. Evidence of the flood caused by the catastrophic failure of the Quail Creek south dike is still visible downstream from the new dam, where the Shanbkaib Member was scoured clean of overlying loose bedrock and sediment.

The dike's failure was principally due to poor foundation design and construction coupled with limited oversight by engineering geologists (O'Neill and Gourley, 1991; Gourley, 1992). Factors that contributed to the failure of the dike included the assumption of a low-permeability foundation, inadequate preparation of the foundation, and placement of unprotected, erodible embankment material on the dam's foundation. The dike was built mostly on the Shnabkaib Member of the Moenkopi Formation, except for the southeast abutment which lies on the "Purgatory Sandstone" of the upper red member. Both of these units contain abundant joints, and the Shnabkaib Member contains abundant gypsum, which readily dissolves in water. Joints allowed water to infiltrate rapidly, creating dissolution channels up to 70 feet (21 m) deep below the dike.

The new dike, called the Quail Creek south dam, was completed in 1990 as a roller-compacted concrete gravity dam (Payton, 1992). The dimensions of the dam are basically the same as the old dike, except that it now includes a new impermeable cutoff trench up to 75 feet (23 m) deep, which is designed to prevent water from seeping under the dam (figure 9).

8 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29

Figure 9. Cutoff trench being excavated at the bottom of the new Quail Creek south dam in January 1990. Photo by Bill Lund, Utah Geological Survey.

After stop, CONTINUE NORTH ALONG UTAH 318. As you head north from the parking lot, note the foot trails in delicate microbiotic soils north of the overlook.

0.5 1.5 Small turn out along east side of road. West of the road, two small, west-dipping thrust faults associated with formation of the Virgin anticline displace the Shnabkaib Member, and, farther north, the upper red member and the Shinarump Conglomerate (figure 10). From the low point in the road just ahead, a kink fold in Shnabkaib strata is visible in a small, steep wash just south of a large talus slope. Much of the slope along the west shore of Quail Creek Reservoir is covered by talus and colluvium, but glimpses of the thrust-faulted rocks are visible as described below.

Figure 10. View north of a small, west-dipping thrust fault that places the Purgatory sandstone on top of itself. The inset shows a small kink fold associated with this west- dipping thrust fault.

9 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah

0.1 1.6 West of the road, the "Purgatory Sandstone" is duplicated by a west-dipping thrust fault. The lower thrust block is just above road level, whereas the main thrust block forms the first high cliff, here stained reddish brown from overlying upper red member strata.

0.2 1.8 The "Purgatory Sandstone" and overlying reddish-brown siltstone and very fine- grained sandstone of the upper red member are steeply west-dipping to nearly vertical in outcrops to the west, where they are in fault contact with gently west- dipping upper red strata.

0.2 2.0 MAIN ENTRANCE TO QUAIL CREEK STATE PARK. Note how the western shore and nearby slopes of Quail Creek Reservoir are mantled by talus. The talus consists of poorly to moderately sorted, angular, clay- to boulder-size, locally derived sediment deposited principally by rock fall. Large blocks of Shinarump and upper red strata characterize talus in this area. The talus grades downslope into colluvium.

0.3 2.3 Boat launch exit.

0.4 2.7 PARK at turnout on east side of road. STOP 2. GENERAL GEOLOGY AT THE NORTH END OF QUAIL CREEK RESERVOIR. The Shinarump Conglomerate Member of the Chinle Formation, seen here on the skyline, forms a resistant, protective cap along the central portion of the Virgin anticline. The Shinarump Conglomerate consists of yellowish-brown sandstone and pebbly sandstone deposited by generally north-flowing braided streams (Stewart and others, 1972; Dubiel, 1994). The streams were probably similar to the modern Platte River and other rivers that drain eastward from the Rocky Mountains and that consist of shallow, interconnected or braided channels and intervening gravel bars. When Shinarump sediments were deposited in the Late Triassic, about 220 million years ago, southwestern Utah was part of a gently north- sloping plain with highlands to the east and west.

The small pebbles found in the Shinarump Conglomerate are mostly chert, quartzite, and quartz. Petrified wood is locally common in coarser, pebbly beds; the logs and limbs are remnants of trees deposited by floods. Much of the Shinarump, however, lacks pebbles and instead consists of sandstone. These sandstones are commonly stained dark brown or black by iron-manganese oxides and locally form "picture stone" or "landscape stone" (figure 11). Shinarump strata are about 100 feet (30 m) thick at Quail Creek State Park.

A pronounced gap in geologic time - about 10 million years - separates the upper red member of the Moenkopi Formation from the overlying, and therefore younger, Shinarump Conglomerate Member of the Chinle Formation. This is the TR-3 regional unconformity of Pipiringos and O'Sullivan (1978), and it separates Early Triassic (Moenkopi Formation) and Late Triassic (Chinle Formation) rocks; it marks a change from mostly shallow-marine to continental sedimentation. In the Quail Creek State Park area, the TR-3 unconformity is a 10 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29

disconformity with minor channeling at the base of the Shinarump Conglomerate Member.

A large, deeply dissected landslide at the north end of Quail Creek Reservoir involves Shnabkaib and upper red strata, and is partly covered by large blocks derived from the Shinarump Conglomerate (figure 6). The landslide is deeply eroded and thus of probable late Pleistocene age, and is characterized by chaotically oriented blocks above the basal slip surface, which is in comparatively weak and unstable, Figure 11. Picture stone from the Shinarump Conglomerate Member of the Chinle Formation, the gypsiferous Shnabkaib strata. same unit that forms the high cliffs around Quail Creek Reservoir. The banding is due to naturally The gentle slope bordering the occurring iron-manganese oxides. This coaster is northwest end of the reservoir is about 4 inches (10 cm) square. covered by mixed alluvial and colluvial deposits of the ancestral Quail Creek (figure 12). These deposits contain large, rounded, granite-like boulders of quartz monzonite porphyry from the Pine Valley Mountains, visible in the distance to the northwest. The Pine Valley Mountains are an early Miocene laccolith intruded into the Tertiary Claron Formation. If the reservoir level is low, fine-grained sand and silt is visible where Quail Creek enters the reservoir, attesting to the ever-present problem of reservoir siltation in the arid southwest.

After stop, CONTINUE NORTHWEST ALONG UTAH 318. Figure 12. Granite-like boulders of quartz monzonite porphyry at the north end of Quail Creek Reservoir. These boulders were eroded from the Pine Valley Mountains and transported nearly 10 miles (16 km) by ancient floods and debris flows to their present location at the north end of Quail Creek Reservoir. Limestone clasts with distinctive star-shaped fossils are also common in these deposits at the north end of the reservoir. The fossils are a type of crinoid, or sea lily, known as Pentacrinus and come from Jurassic rocks that crop out on the flanks of the Pine Valley Mountains.

11 R. F. Biek Geological Road Guide To Quail Creek State Park, Washington County, Utah

0.2 2.9 Drive through the water gap formed by the Shinarump Conglomerate on the west limb of the Virgin anticline, and onto old alluvial deposits. Note brightly colored swelling mudstone of the Petrified Forest Member, capped by terrace gravels.

0.2 3.1 JUNCTION OF UTAH 318 WITH I-15 FRONTAGE ROAD.

END OF ROAD LOG

REFERENCES

Biek, R.F., 1997, Interim geologic map of the Harrisburg Junction quadrangle, Washington County, Utah: Utah Geological Survey Open-File Report 353, 124 p., scale 1:24,000.

—–1998, Interim geologic map of the Hurricane quadrangle, Washington County, Utah: Utah Geological Survey Open-File Report 361, 154 p., scale 1:24,000.

—–1999, The Geology of Quail Creek State Park: Utah Geological Survey Public Information Series 63, 21 p.

Dubiel, R.F., 1994, Triassic deposystems, paleogeography, and paleoclimate of the Western Interior, in Caputo, M.V., Peterson, J.A., and Franczyk, K.J., editors, Mesozoic systems of the Rocky Mountain region, USA: Rocky Mountain Section of Society of Economic Paleontologists and Mineralogists, p. 133-168.

Gourley, Chad, 1992, Geological aspects of the Quail Creek dike failure, in Harty, K.M., editor, Engineering and environmental geology of southwestern Utah: Utah Geological Association Publication 21, p. 17-38.

O'Neill, A.L., and Gourley, Chad, 1991, Geologic perspectives and cause of the Quail Creek dike failure: Bulletin of the Association of Engineering Geologists, v. 28, no. 2, p. 127-145.

Payton, C.C., 1992, Geotechnical investigation and foundation design for the reconstruction of Quail Creek dike, in Harty, K.M., editor, Engineering and environmental geology of southwestern Utah: Utah Geological Association Publication 21, p. 39-51.

Pipiringos, G.N., and O'Sullivan, R.B., 1978, Principal unconformities in Triassic and Jurassic rocks, western Interior United States - a preliminary survey: U.S. Geological Survey Professional Paper 1035-A, 29 p.

Proctor, P.D., 1953, Geology of the Silver Reef (Harrisburg) mining district, Washington County, Utah: Utah Geological and Mineral Survey Bulletin 44, 169 p.

Proctor, P.D., and Brimhall, W.H., 1986, Silver Reef mining district, revisited, Washington County, Utah, in Griffen, D.T., and Phillips, W.R., editors, Thrusting and extensional structures and mineralization in the Beaver Dam Mountains, southwestern Utah: Utah Geological Association Publication 15, p. 159-177. 12 P.B. Anderson and D.A. Sprinkel, editors 2000 Utah Geological Association Publication 29

Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy and origin of the Triassic Moenkopi Formation and related strata in the Colorado Plateau region, with a section on sedimentary petrology by R.A. Cadigan: U.S. Geological Survey Professional Paper 691, 195 p., scale 1:2,500,000.

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