PAUL AVERITT U. S. Geological Survey, Denver, Colo.

Upper Tertiary Surficial Deposits

near Cedar City, Iron County,

Abstract: Along the Hurricane fault in south- terrace on the east, or upthrown side of the fault. western Utah, fanglomerate, pediment, and stream- Much of the difference is the result of displacement channel deposits ranging in age from Miocene(?) to on the fault in Pliocene and Pleistocene time. Dif- Recent have been dated through studies of the ferences in composition of gravel also establish the composition and size of gravel components and existence of an approximate late Tertiary drainage distance from sources of materials. The deposits divide between two westward-flowing streams that range in elevation from 6000 feet at the base of the formerly headed about 8 miles east of the Hurricane Hurricane Cliffs on the west, or downthrown side fault. The channels of these streams have since been of the Hurricane fault, to 9000 feet on the Kolob obliterated by uplift, erosion, and basalt flows.

CONTENTS Introduction 37 Plate Facing Deposits on Kolob terrace 40 1. Abandoned stream-channel deposits on Kolob Abandoned stream-channel deposits 40 terrace, southwestern Utah 42 Urie Creek pediment deposit 41 2. Coarse gravel in abandoned stream-channel de- Fanglomerate deposits at base of Hurricane Cliffs 41 posits and Urie Creek pediment, south- Conclusions 44 western Utah 43 References cited 44 Figure Table 1. Outline map of southeastern Iron County, 1. Diagnostic volcanic rocks in surficial deposits Utah, showing upper Tertiary snrficial near Cedar City, Iron County, Utah... 42 deposits and section 38

(A) Abandoned stream-channel deposits INTRODUCTION (B) Urie Creek pediment deposit The Hurricane fault in southwestern Utah (2) Deposits at the base of the Hurricane has been active since Miocene(?) time. At Cliffs on the downthrown (west) side of Cedar City, near the north end of the fault, the the Hurricane fault at elevations of total displacement is 8000-10,000 feet. As a about 6000 feet consequence of the prolonged movement and (A) Cross Hollow Hills fanglomerate the large displacement, an enormous amount deposit of material has been eroded from the upthrown (B) North Hills fanglomerate deposit block and transported westward to the Great The Cross Hollow Hills and North Hills Basin and southward to the . fanglomerate deposits have been described by Part of this material has been deposited on both Thomas and Taylor (1946) and by the writer the upthrown and downthrown sides of the (Averitt, 1957; 1962, p. 35-37). the present Hurricane fault. Most of the surficial deposits paper is based on recent work and provides a are Quaternary, but a few of distinctive com- more complete statement concerning the origin position or of unusually high altitude are of and the relationships between the deposits. upper Tertiary. These deposits and the vertical relationship The upper Tertiary deposits may be grouped between the Urie Creek pediment deposit and into the following categories: the Cross Hollow Hills fanglomerate deposit (1) Deposits on the Kolob terrace on the are shown on Figure 1. upthrown (east) side of Hurricane fault The Kolob terrace (Fig. 1) forms a broad at elevations of about 9000 feet bench between the Hurricane Cliffs on the

Geological Society of America Bulletin, v. 75, p. 37-44, 1 fig., 2 pis., January 1964 37

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west and cliffs developed on the Wasatch For- early Eocene age, volcanic rocks of inter- mation of early Eocene age on the east. The mediate composition of Eocene (?) to early terrace is developed on nonresistant beds in Miocene(?) age, and basalt of Quaternary age. the Wahweap Sandstone of Late Cretaceous These gravel deposits formed at the foot of age. It is now highly dissected by Crystal Creek, the precipitous Wasatch Cliffs at a time when Deep Creek, and other southward-flowing the cliffs stood farther west than at present. tributaries of the Virgin River, but upland The process by which the ridges were formed is surfaces locally exhibit a gently rolling, mature going on today at the base of the present Wa- topography that is considered to be relic of an satch Cliffs. The familiar sequence of events is earlier stage in the erosion cycle (Gregory, as follows: A steep, V-shaped valley is formed 1950, p. 134; Pi. 46; Averitt, 1962, p. 45-46; initially by headward erosion of the swift- Fig. 14). moving streams heading in the cliffs. The gra- The cliffs developed on the Wasatch Forma- dient of the valley is very steep at the head but tion, hereinafter termed the Wasatch Cliffs, lie becomes less steep at the base of the cliffs. At mostly east and northeast of the area shown on the point where the gradient flattens, the valley Figure 1 and stand 1000-2000 feet above the becomes filled with heterogeneous material Kolob terrace. At many places east and north- washed in from above and from the sides. The east of this area the Wasatch Cliffs are capped accumulated material in the valley bottom is by volcanic rocks of intermediate composition highly permeable. Flowing water sinks into this and of Eocene (?) to early Miocene (?) age and material, is slowed to a trickle, and thus loses by basalt flows of Quaternary age. its erosive power. During periods of heavy The surficial deposits were derived in con- runoff the water in the channel flows on the siderable part from the Wasatch Formation sides of the gravel filling and in time cuts below and from the overlying volcanic rocks. The and isolates it. several classes of surficial deposits are dis- The preserved high-level channels range cussed separately. outward from the present Wasatch Cliffs according to age; the oldest channels are 5 DEPOSITS ON KOLOB TERRACE miles west of the cliffs. This age relationship is confirmed by the composition of the channel Abandoned Stream-Channel Deposits gravels. In the Kolob terrace-Hurricane fault The deposits interpreted as abandoned region, volcanic rocks of intermediate com- stream-channel deposits are shown in black on position are uniformly older than basalt Figure 1. These deposits are the highest on (Gregory, 1950, p. 97). Whereas the older vol- the Kolob terrace. They cap long narrow ridges, canic rocks of intermediate composition are some of which are more than 1000 feet above considered to be Eocene(?) to early Miocene(?) present drainage. Considered individually and (Mackin, 1960, p. 97-104), the basalt is con- collectively the deposits are very streamlike in sidered to be Quaternary (Gregory, 1950, p. length, width, slope, spacing, and orientation. 100). The oldest basalt may be late Tertiary Plate 1 shows longitudinal and side views of (Thomas and Taylor, 1946, p. 33, 34; Cook, two prominent ridges, and Figure 1 of Plate 2 1957, p. 69); the youngest is certainly Recent. shows the typical coarse gravel on a third ridge. The older abandoned stream-channel de- This ridge is half a mile long and is as straight posits contain abundant volcanic material of and narrow as a railroad embankment. The intermediate composition but no basalt. Be- crest slopes northwest with a gradient of about cause of their lack of basalt and their distance 400 feet per mile. The view in Figure 1 of from the parent Wasatch Cliffs these deposits Plate 2 is of the eroded southeast end of the are considered to be Miocene or Pliocene. ridge. The younger deposits, which are considered to The material in the abandoned stream- be Quaternary, either contain basalt in abun- channel deposits ranges in size from coarse sand dance or head against the Wasatch Cliffs at to boulders 12 feet in diameter. Material finer points where there is no basalt but where their than coarse sand is inconspicuous. The pebbles comparatively recent age is immediately ap- and cobbles are well rounded, the small boul- parent. Basalt outcrops are not shown on ders are subrounded, and the large boulders are Figure 1 because basalt is widespread and abun- subangular to angular. The material was derived dant in the region and the additional pattern from the Kaiparowits Formation of Late would clutter the illustration. Cretaceous age, the Wasatch Formation of The older, prebasalt, stream gravel deposits

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can be divided further into a northern and a ponents decrease in size from boulders 10 feet southern group on the basis of a consistent in diameter at the upper, east end of the de- difference in the contained volcanic material. posit to boulders lJ/£ or 2 feet in diameter in The northern deposits contain two diagnostic the middle to cobbles and pebbles at the lower, volcanic rocks. Most abundant and most charac- west end. teristic are cobbles and boulders of the Baldhills The Urie Creek pediment deposit is several Member of the Isom Formation (Mackin, I960, hundred feet lower and correspondingly young- p. 90, 99). This rock has been mapped in eastern er than the abandoned stream-channel deposits Iron County, northeast of the map area, as the immediately to the north and south, but it is latite at Black Ledge (Gregory, 1950, Pis. 2, also prebasalt in age, because it lacks basalt 29) and in the Granite Mountain area of the fragments and is overlain by flows of basalt Iron Springs district, west of the map area, as on its southeast corner. Like the nearby aban- member A of the volcanic sequence (Mackin, doned stream-channel deposits, it was formed 1954). Less abundant, but common in the north- at a time when the Wasatch Cliffs stood farther ern group of deposits, are cobbles and small west than at present. The Urie Creek pedi- boulders of the basal glass of the Leach Canyon ment required a temporary base level for its Tuff [Member] of the Quichapa Formation formation. Itspresent position high on a drain- (Mackin, 1960, p. 90). This rock has been age divide in an area of relic mature topography mapped as member C of the volcanic sequence is anomalous. If the dip on the base of the gravel i n the G ranite Mountain area of the Iron Springs on the pediment is projected westward to the district (Mackin, 1954). It also forms the crest Hurricane fault line, the projected plane lies of the mountain at Brian Head in sec. 12, T. about 1500 feet above the desert basin. Inas- .36 S., R. 9 W.. about 4 miles north of the much as displacement on the Hurricane fault northeast corner of the map area (Fig. 1). has increased intermittently throughout late The southern deposits contain conspicuous Tertiary and Quaternary time (Averitt, 1962, cobbles and boulders of the Kolob Latite as p. 41), it seems certain that at the time of recently defined by the writer in the Cedar deposition the vertical distance between the Mountain quadrangle (Averitt, 1962, p. 30). Urie Creek pediment and the desert basin to A small outcrop of this rock occurs in sec. 17, the west was much less than at present. T. 37 S., R. 10W. but has been omitted from Figure 1 because it is not essential to the dis- FANGLOMERATE DEPOSITS AT cussion of the surficial deposits. BASE OF HURRICANE CLIFFS The characteristic features of these three At the base of the Hurricane Cliffs, 8 miles diagnostic rocks are summarized in Table 1, west and 3000 feet lower than the Urie Creek and a line on Figure 1 separates the two groups pediment deposit and other surficial deposits of deposits. on the Kolob terrace, are two large fanglom- erate deposits, each covering 5 or 6 sq mi, Urie Creef^ Pediment Deposit which have been mapped by Thomas and The Urie Creek pediment deposit covers Taylor (1946, p. 33; PL 3). These deposits 1}^2 scl rni near the center of the map area form the tops of low hills rising above the desert (Fig. 1). The base of the deposit is about 9300 basin to the west. The Cross Hollow Hills feet above sea level at the highest end, and it (Fig. 1) rise 300 feet above the basin, and the slopes to the west at about 200 feet per mile. North Hills rise 500 feet above the basin. The pediment lies high on a major drainage The two deposits are part of an uplifted divide between Coal Creek, a westward- block, or horst, separated from the Hurricane flowing stream draining into the , Cliffs by an alluviated graben half a mile to 1 and the West Fork of Deep Creek, a southward- mile wide (Thomas and Taylor, 1946, PI. 3). flowing tributary of the Virgin River (PI. 2, The several streams issuing from the Hurricane fig. 2). Cliffs skirt the edges of the deposits. However, The deposit contains cobbles and boulders of Green Hollow Creek, a relatively recent stream, the Baldhills Member of the Isom Formation built a fan across the alluviated valley and for a (Mackin, 1960) and of the basal glass of the period flowed across the Cross Hollow Hills Leach Canyon Tuff [Member] of the Quichapa by way of Cross Hollow Creek. Green Hollow Formation (Mackin, 1960) and thus is related Creek has since been diverted southward. to the northern group of older abandoned The two fanglomerate deposits are composed stream-channel deposits. The largest com- primarily of the same rock types observed in the

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/1/37/3416950/i0016-7606-75-1-37.pdf by guest on 29 September 2021 c r TABLE 1. DIAGNOSTIC VOLCANIC ROCKS IN SURFICIAL DEPOSITS NEAR CEDAR CITY, IRON COUNTY, UTAH ;> <* cu 70 Groundmass Plagioclase phenocrysts surficial volcanic Texture and Size Per cent Compo- \ deposits rocks Color composition (in mm) of rock sition Color C Baldhills Medium dark Aphanitic 1-3 avg.; 15 Calcic White Conspicuous layers ^-2 inches £, Member of gray to 5 max. thick. Weathered surfaces pitted , I so in grayish red by loss of phenocrysts pj Formation* TO MiNo r tnert-I n H Leach Canyon Reddish brown Aphanitic Basal glass of welded tuff. Con- £j Tuff [Member] tains many 1—2-m m fragments of *< of Quichapa lithic materials and crystals ^ Formation* C Kolob Light gray Microgranular 2-5 avg. ; 40-45 Intermedi- Light Over-all coarse, granular texture "j Latitet or intergrowth 15 max. ate. gray because of preponderance of ;> Southern pinkish gray of quartz and AbsAns phenocrysts f orthoclase a npi O 'Mackin (1960, p. 90, 99) '£ t Averitt (1962, p. 30) En G X

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/1/37/3416950/i0016-7606-75-1-37.pdf by guest on 29 September 2021 Figure 1. Abandoned stream-channel deposit on ridge in sec. 36, T. 37 S., R. 10 W. Look- ing northwest

Figure 2. Side view of ridge in sec. 4, T. 37 S., R. 10 W., capped by abandoned stream-channel deposit. Closeup of part of crest shown in inset. Tributary of Urie Creek in foreground. Looking north

ABANDONED STREAM-CHANNEL DEPOSITS ON KOLOB TERRACE SOUTHWESTERN UTAH

AVERITT, PLATE 1 Geological Society of America Bulletin, volume 75

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/75/1/37/3416950/i0016-7606-75-1-37.pdf by guest on 29 September 2021 Figure 1. Typical coarse gravel of abandoned stream-channel deposit on ridge in sees. 16 and 17, T. 37 S., R. 10 W. Looking southeast. Lower Kolob terracein distance

Figure 2. Eastern edge of the Urie Creek pediment near skyline, 1100 feet above Coal Creek in foreground. Knoll on right skyline is capped by pediment gravel. Thin white line just below skyline and left of knoll is base of gravel. Pediment dips west away from viewer. Wasatch Cliffs are behind viewer about 4 miles east of eastern edge of ped- iment. View is from point in sec. 12, T. 37 S., R. 10 W.

COARSE GRAVEL IN ABANDONED STREAM-CHANNEL DEPOSITS AND URIE CREEK PEDIMENT, SOUTHWESTERN UTAH

AVERITT, PLATE 2 Geological Society of America Bulletin, volume 75

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prebasalt surficial deposits on the Kolob ter- the bulk of the fanglomerate deposits was laid race, and they exhibit the same marked dif- down at the base of an ancestral cliff at or near ference in contained volcanic material. The the position of the present Hurricane Cliffs, Cross Hollow Hills deposit is clearly related to which at an early stage in uplift exposed beds of the northern group of deposits on the Kolob Cretaceous and possibly older age at the base, terrace, and the North Hills deposit is clearly overlain in turn by the Wasatch Formation of related to the southern group of deposits. early Eocene age and the volcanic rocks of This is shown by the line on Figure 1. Scattered Eocene(?) to early Miocene(?) age. Gardner over the fanglomerate deposits and concen- (1941, p. 251) has presented other evidence for trated locally in channels are small amounts of such an ancestral cliff. material from the Carmel Formation and Inasmuch as the bulk of material in the Cross Navajo Sandstone, which are exposed in the Hollow Hills and North Hills fanglomerate middle of the Hurricane Cliffs (Fig. 1). This deposits could not have been supplied by Green material is probably a later addition to the Hollow and Murie Creeks, which rise in the deposits brought in by a process of alluviation present Hurricane Cliffs, the work must have like that described for Green Hollow Creek. been done by older, ancestral streams whose The fanglomerate deposits contain no basalt channels have since been obliterated by uplift, fragments, but are overlain by basalt flows at erosion, and basalt flows. That such streams many places. formerly existed may be deduced from several Large boulders are common in the fanglom- lines of evidence. The conspicuous difference in erate deposits. The maximum long dimensions composition of volcanic rocks in the northern as related to the individual deposit and to rock and southern groups of surficial deposits sug- type are as follows: gests two westward-flowing streams with a drainage divide near the line on Figure 1. Baldhills Member of the The alignment of the Urie Creek pediment and Isom Formation, 10 Cross Hollow Hills of the nearby abandoned stream-channel de- feet deposit posits suggests the headwaters of a former Wasatch limestone, 8 westward-flowing stream at about the position feet of Green Hollow. The barbed drainage at the Kolob Latite, 14 feet head of Crystal Creek (Fig. 1) marks the for- North Hills deposit Wasatch limestone, 10 mer head of a westward-flowing stream an- feet cestral to Murie Creek. Other evidence for the existence of an ancestral Murie Creek has been In general, the larger boulders in the fanglom- presented previously (Averitt, 1962, p. 36). erate deposits are about the same size as boul- The several lines of evidence strongly sup- ders of the same composition in the abandoned port the conclusion that the bulk of material stream-channel deposits and in the upper part in the fanglomerate deposits on the Cross of the Urie Creek pediment deposit but much Hollow and North Hills was deposited at a very larger than boulders in the middle and lower early stage in the development of the Hurricane parts of the Urie Creek pediment deposit. Cliffs and is, therefore, the oldest visible sur- This size relationship proves that the Cross ficial material in the region. The two fanglom- Hollow Hills fanglomerate deposit is not a erate deposits are demonstrably older than westward extension of the Urie Creek pedi- the Urie Creek pediment deposit, which be- ment deposit. The relatively large size of the cause of its distance from the present Wasatch boulders in the two fanglomerate deposits Cliffs and the absence of basalt fragments in proves that they were laid down very near the the gravel, is considered to be Miocene or source of material and near the base of an es- Pliocene. In view of the fact that between carpment like the Hurricane Cliifs or the Wa- deposition of the two fanglomerate deposits satch Cliffs. The predominance in the fanglo- and the younger Urie Creek pediment deposit, merate deposits of material characteristic of the ancestral Wasatch Cliffs retreated 8 miles the Wasatch Cliffs proves that the bulk of the from the Hurricane fault line to the head of the fanglomerates was not laid down at the base of pediment, the fanglomerate deposits are prob- the present Hurricane Cliffs, because the pres- ably Miocene. The youngest volcanic rocks ent cliffs yield only debris of basalt and of broken by the first movement on the Hurricane Cretaceous and older rocks. Therefore, the fault are considered by Mackin (1960, p. 98) accumulated evidence clearly establishes that to be early Miocene(P). The demonstrated age

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of the Cross Hollow and North Hills deposits Material of this composition and age normally supports and is supported by the supposition would be deeply buried in the bolson deposits that the first movement on the Hurricane fault at the base of the Hurricane Cliffs but has been took place in early or middle Miocene time exposed in the two deposits because of their following deposition of the volcanic rocks and position on an uplifted structural block. that the deposition of the fanglomerate material During an ensuing period of erosion the an- took place shortly thereafter. cestral Wasatch Cliffs retreated eastward 8 Some material was added to the fanglomerate miles. As a consequence of this retreat a mature deposits by subsequent uplift and erosion of topography developed between the Wasatch rocks in the Hurricane Cliffs and possibly by Cliffs and the Hurricane fault line. At the 8- removal and redeposition of younger surficial mile position a period of temporary stability material from the Kolob terrace. However, the resulted in formation of the Urie Creek pedi- amount of such younger material is very small ment at the base of the cliffs. The period of as compared to the bulk of older material. stability was ended by renewed movement on the Hurricane fault, which formed a new cliff CONCLUSIONS exposing older rocks at the fault line, accelerat- The several categories of older surficial de- ed eastward retreat of the Wasatch Cliffs, and posits clearly record a long period in the early inaugurated a period of dissection of the up- development of the Hurricane fault and the lifted Kolob terrace. Kolob terrace. In summary, the first major The stream-channel deposits were formed movement on the Hurricane fault in early or more or less continuously at the base of the middle Miocene time resulted in the formation retreating Wasatch Cliffs. The group shown of the ancestral Wasatch Cliffs at the present on Figure 1 has persisted to the present time fault line. These cliffs provided the debris primarily because of its position on a major making up the bulk of material in the Cross drainage divide between Great Basin and Colo- Hollow and North Hills fanglomerate deposits. rado River drainage.

REFERENCES CITED Averitt, Paul, 1957, Sequence of late Tertiary events on the Kolob Terrace, Iron County, Utah, as inter- preted by elevated surficial deposits (Abstract): Geol. Soc. America Bull., v. 68, p. 1857-1858 1962, Geology and coal resources of the Cedar Mountain quadrangle, Iron County, Utah: U. S. Geol. Survey Prof. Paper 389, 72 p. Cook, E. F., 1957, Geology of the Pine Valley Mountains, Utah: Utah Geol. Mineralog. Survey Bull. 58, 111 p. Gardner, L. S., 1941, The Hurricane fault in southwestern Utah and northwestern : Am. lour. Sci., v. 239, p. 241-260 Gregory, H. E., 1950, Geology of eastern Iron County, Utah: Utah Geol. Mineralog. Survey Bull. 37, 153 p. Mackin, J. H., 1954, Geology and iron ore deposits of the Granite Mountain area, Iron County, Utah: U. S. Geol. Survey Mineral Inv. Field Studies Map MF-14 1960, Structural significance of Tertiary volcanic rocks in southwestern Utah: Am. Jour. Sci., v. 258, p. 81-131 Thomas, H. E., and Taylor, G. H., 1946, Geology and ground-water resources of Cedar City and Parowan Valleys, Iron County, Utah: U. S. Geol. Survey Water-Supply Paper 993, 210 p.

MANUSCRIPT RECEIVED BY THE SOCIETY, APRIL 16, 1963 PUBLICATION AUTHORIZED BY THE DIRECTOR, U. S. GEOLOGICAL SURVEY

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