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Geology
The rocks underlying Red Butte Canyon range in age from recent Holocene deposits of our time to Mississippian rocks that are about 360 million years old. Holocene and Pleistocene deposits are unconsolidated, consisting mostly of landslides or alluvium deposited by existing streams. Their aerial distribution is shown in Figure 3, and a description of the deposits is listed in Table 1. For an interactive map with descriptions, please click here.
Fig. 3. Geological map of Red Butte Canyon Research Natural Area. See Table 1 for a description of abbreviations. Solid lines represent contacts between formations, dashed lines represent normal faults, and T-dashed lines represent the Black Mountain thrust fault. The transect A-A' is shown in cross section to Figure 4. Adapted from Marsell and Threet (1960) and Van Horn and Crittenden (1987).
The older rocks range in age from Mississippian to Jurassic, a span of about 220 million years. They are all consolidated now, but originally they were formed as deposits in oceans or inland seas or as sand dunes in an arid environment. No rocks representing the approximately 140 million years between the end of Jurassic time and the Holocene are presented in Red Butte Canyon. Either they were never deposited or they have been eroded.
The consolidated rocks in most parts of the lower walls of the canyon consist chiefly of shale, with some gritty quartzite and sandstone. The upper southeast-facing slopes consist mostly of limestone with some sandstone and limy shale. The upper northwest-facing slopes are made up mostly of sandstone with limestone and limy shale near the southeast divide. Figure 3 shows the distribution of the rocks in the canyon, and they are described in Table 1.
The older consolidated rocks in the canyon generally dip toward the southeast (Figure 4), and they form the northern flank of a large syncline whose axis trends toward the northeast and whose southern flank is in Mill Creek Canyon, about 6.5 km to the south. The rocks are cut by numerous normal faults that are part of the Wasatch fault zone, a lengthy fault zone that bounds the west face of the Wasatch Range for almost its entire length. Movement along these normal faults has resulted in horizontal displacement of the rock formations, whereas movement along the Black Mountain thrust fault in the northwestern part of the canyon has raised older rocks to a position overlying younger rocks. The faults and their effects on the consolidated rocks are shown Figures 3 and 4.
 Fig. 4. Geologic cross section of Red Butte Canyon. Explanation as in Figure 3. Adapted from Van Horn and Crittenden (1987). |
Cenozoic era, Quaternary system, Holocene series
fa Flood-plain alluvium. Sand, cobbly to silty, dark gray at top; grading downward to medium to light gray, sandy to cobbly gravel; locally bouldery.
fe Engineered fill. Selected earth material that has been emplaced and compacted.
Cenozoic era, Quaternary and Tertiary systems, Holocene and Pleistocene series
fg Alluvialfan deposits. Bouldery to clayey silt, dark gray to brown; rocks angular to subrounded.
ld Landslide deposits. Composition similar to material upslope.
Mesozoic era, Jurassic system
Jtc Twin Creek Limestone. Brownish gray and pale gray to pale yellowish gray silty limestone, intercalated with greenish gray shale.
Mesozoic era, Jurassic? and Triassic? systems
JTn Nugget Sandstone. Pale pinkish buff, fine- to medium-grained, well-sorted sandstone that weathers orange-brown. Massive outcrops form the ridge called Red Butte.
Mesozoic era, Trassic system
Tau Ankareh Formation, upper member. Reddish brown, reddish purple, grayish red, or bright red shale, siltstone, and sandstone.
Tag Ankareh Formation, Gartra Grit Member. White to pale purple, thick-bedded, crossbedded, pebbly quartzite. Forms a prominent white ledge for long distances.
Tam Ankareh Formation, Mahogany Member. Reddish brown, reddish purple, grayish red, or bright red shale, siltstone, and sandstone.
Tt Thaynes Formation. Medium to light gray, fossiliferous, locally nodular limestone, limy siltstone, and sandstone.
Tw Woodside Shale. Grayish red, grayish purple or bright red shale and siltstone.
Paleozoic era, Permian system
Ppc Park City Formation and related strata. Fossiliferous sandy limestone, calcareous sandstone, and a medial phosphatic shale tongue.
Paleozoic era, Pennsylvanian system
Pw Weber Quartzite. Pale tan to nearly white, fine- to medium-grained, crossbedded quartzite and medium gray to pale gray limtestone.
Prv Round Valley Limtestone. Pale gray limtestone with pale gray siltstone partings. Contains pale pinkish chert that forms irregular nodules.
Paleozoic era, Mississippian system
Mdo Doughnut Formation. Medium gray, thin-bedded limestone with pods of dark gray to black chert and abundant brachiopods and bryozoa.
Mgb Great Blue Formation. Thick-bedded, locally cliff-forming, pale gray, fine-grained limtestone.
Mh Humbug Formation. Alternating, tan-weathering, limy sandstone and limestone or dolomite.
Md Deseret Limestone. Thick ledges of dolomite and limtestone with moderately abundant lenses and pods of dark chert.
Paleozoic era
P Paleozoic rocks, undifferentiated.