U.S. DEPARTMENT OF THE INTERIOR MISCELLANEOUS FIELD STUDIES MAP MF–2351 U.S. GEOLOGICAL SURVEY Version 1.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 109°30' 109°15' DRY GR VALLEY Westwater Church Canyon Rock Westwater Member Canyon 6 191 Member Draw 38°00' NC Harts19 Recapture Member 17 Recapture Member 7 ABAJO MOUNTAINS 18 Salt Wash Member and younger rocks 16 bed RA Monticello M bed RB O Salt N T 15 666 Wash E Z Recapture Member Member U 8 M GR A bed RC 8 C 14 A N 0 NC 13 Y 37°45' O GR N GR Mancos GR Salt Wash Member and younger rocks 0 Jim GR GR Butte 12 1 GR ater Canyon 9 GR stw UTAH 7 We 9 Black Steer 9 of COLORADO GR Member MORRISON FORMATION (part) MORRISON FORMATION SP Knoll 11 1 SP 10 limit Tidwell Member 8 10 Blanding northern 1 Bluff Sandstone Member k e 2 Approximate e 10 r 10 9 C 10 8 5 (part) MORRISON FORMATION 10 J-5 upper 191 J-5 unconformity Tidwell 10 Member 8 bed A unconformity member bed A 2 Bluff Sandstone Member 11 Black Mesa e 9 Member 37°30' r Horse Mesa Member u Mesa Butte t upper Horse Wanakah k p e a 7 member upper member Formation e bed V c middle r 2 bed V member e C middle member bed V R 11 3 WANAKAH 6 FORMATION 11 9 11 Wash siltstone a bed siltstone 11 11 262 member m at member u Butler COMB RIDGE 3 z 12 e 6 t 10 n o M lower member WANAKAH FORMATION WANAKAH 3 5 NC Slick Rock Member 4 salmon sandstone 7 12 4 12 10 12 12 12 4 Member Bluff 2 Rehoboth 13 1 3 Montezuma 11 JUAN Creek Rehoboth Member Rehoboth 37°15' AN RIVER J-2 unconformity Member S ENTRADA 4 middle sandstone SANDSTONE ENTRADA SANDSTONE ENTRADA sandstone GROUP SAN RAFAEL middle 13 5 Aneth SAN RAFAEL GROUP SAN RAFAEL 11 8 Navajo Sandstone 13 13 13 13 5 Formation 14 Carmel Dewey 12 J-2 0 5 10 15 20 25 MILES Bridge unconformity 5 Navajo Sandstone EXPLANATION FOR LINE OF SECTION Member 0 5 10 15 20 25 30 KILOMETERS FEET EXPLANATION 0 CARMEL FORMATION Drill hole CARMEL FORMATION Depth, in hundreds of feet, Sandstone - Massive or flatbedded 11 below surface in drill hole Measured section Outcrop of Recapture Member Sandstone - Crossbedded SP Spontaneous potential curve 50 LINE OF SECTION of Morrison Formation 6 Siltstone - Variably sandy. Includes GR Gamma-ray curve Figure 1. Index map showing locations of drill holes and measured sections. Distribution (No horizontal scale) thin clay and sandstone beds 100 NC Boundary of stratigraphic of Recapture Member and approximate northern limit of Westwater Canyon Shale - Variably silty nomenclature change Member of Morrison Formation from Haynes and others (1972). Correlation line Unconformity 200 114° 42° 112° 123456 789101112131415161718 19 ° ° * 110 108 106° 104° Westwater* * Canyon Member Salt Lake City Vernal DNM bed RA FEET Eastern limit of Recapture bed NC ° * * Morrison 0 40 Carmel Formation * RC Salt Wash Formation Morrison bed Member Member 50 Denver Salt Wash Member and younger rocks (part) UTAH RB NC 100 Formation Grand (part) Junction * Tidwell 200 SRS DB Bluff Sandstone Member Member COLORADO J-5 unconformity Tidwell Member Moab Horse Mesa Member and upper member 300 Limit of Dewey Bridge Member * Wanakah Formation Wanakah * middle member 38° of Carmel Formation at Formation bed * Butler Wash siltstone 400 Area of lower member NC member Entrada Slick Rock Member Dove * * figure 1 * salmon sandstone * * Sandstone Entrada Creek Rehoboth Sandstone Entrada Sandstone * Member * Rehoboth Member middle sandstone * * * J-2 unconformity middle sandstone Mexican Carmel Formation Water Farmington Navajo Sandstone Dewey Bridge Member Navajo Sandstone 36° of Carmel Formation ARIZONA Eastern limit of NEW MEXICO Carmel Santa Fe Formation Gallup Vertical exaggeration about x70 Rehoboth * Thickness is average of adjacent sections 0 5 10 15 20 MILES NC, Boundary of stratigraphic nomenclature change 0 50 100 150 200 MILES 0 20 30 KILOMETERS 10 0 100 200 300 KILOMETERS Figure 2. Map showing location of study area. DB, Dewey Bridge; RESTORED STRATIGRAPHIC DIAGRAM DNM, Dinosaur National Monument; SRS, San Rafael Swell. NOTE nearby on the ancient Causeway High, and these strata may also grade northward into The Slick Rock Member overlies the Rehoboth Member throughout much of the study about 800 ft thick near Bluff (Fred Peterson, written commun., 1999) and is 750–800 ft one-half to two-thirds of the Salt Wash. Between these sandstone lenses are red mudstone name they abandoned), were assigned to the Salt Wash Member; (5) a restricted Recapture Table 1. Number, name, and location of drill holes and measured sections similar beds of sandstone in the subsurface. The formation thins northward and is now not area. The member is mainly a fine-grained to very fine grained sandstone, but it contains thick in Dry Valley (Weir and others, 1994). units containing some thin beds of very fine grained sandstone. This alternation of cliffs of Member—a revision that reduced the member to about 30 percent of the unit defined by [The following U.S. Geological Survey topographic maps, scale 1:62,500, were used to The Middle Jurassic San Rafael Group and the Upper Jurassic Morrison Formation recognized as far north as the Shell Oil Co. drill hole (sec. 5), 9 mi northeast of Bluff. disseminated sparse, coarse to very coarse, well-rounded grains of clear quartz. The coarse In the study area, only the Bluff Sandstone Member, Tidwell Member, and lower part of resistant sandstone and debris-covered slopes underlain by less resistant mudstone units Gregory (1938, p. 58)—was included in the Bluff Sandstone of their revised San Rafael locate sections measured in the field: Blanding (1957); Bluff (1962); Montezuma Creek consist mainly of sandstone, siltstone, and shale. The San Rafael Group is widely displayed The Carmel Formation north of Monticello consists solely of strata that are laterally grains, which are informally termed “Entrada berries,” contrast markedly with the fine- the Recapture Member were examined in the field. Accordingly, the line of section and the produces a steplike cliff characteristic of the Salt Wash Member.” In Montezuma Canyon, Group; and (6) the Tidwell Member, in the San Rafael Swell where it directly overlies type (1962); Monticello (1957); Monument Canyon (1957)] around Bluff (fig. 1) in the southern part of the study area and along Harts Draw and Dry equivalent to the Dewey Bridge Member, heretofore of the Entrada. In the San Rafael Swell grained matrix. The Slick Rock Member was deposited in a sequence of alternating restored stratigraphic diagram show only the lower part of the Morrison Formation. the Salt Wash Member ranges in thickness from 320 to 520 ft (Huff and Lesure, 1965, p. Summerville, was assigned to the Summerville Formation. ________________________________________________________________________________ Valley in the northern part. Along Montezuma Canyon, which is almost 1,500 ft deep, the (fig. 2) of east-central Utah, the formation comprises gray and red siltstone and shale and crossbedded and flatbedded units. The crossbedded units are eolian deposits (Shawe and Additional details provided by published reports and a written communication from Fred 24); in Dry Valley, the member is 350–425 ft thick (Weir and others, 1994). In contrast, the nomenclature of the Morrison as used herein follows that originally Section Name Location upper part of the group crops out for about 10 mi; at one locality (sec. 13, fig. 1) all of it is subordinate gray sandstone, gypsum, and marine limestone. Eastward from the San Rafael others, 1968, p. A41–A45). The member averages about 162 ft in thickness, ranging from Peterson (1999) supplement the description of the Morrison Formation in the present described by Gregory (1938). The Recapture and Westwater Canyon Members are retained No. exposed. Elsewhere in the study area, younger rocks conceal the San Rafael Group. The Swell, the lower part disappears by progressively lapping onto the J-2 unconformity. The 145 ft at the Houston Oil and Gas and Minerals Corp. drill hole (sec. 15) to 206 ft at Harts report, and further details are in reports by Craig and others (1955), Huff and Lesure WESTWATER CANYON MEMBER as mapped in the Bluff–Montezuma Canyon area by Cooley and others (1969), Haynes and __________________________________________________________________________________________ Morrison Formation is also generally well exposed throughout the area. From near upper part grades into the Dewey Bridge Member in a transition zone 2–5 mi wide about 35 1 measured section (sec. 19). (1965), Weir and others (1994), and Witkind (1964). others (1972), Huff and Lesure (1965), and O’Sullivan (1965). 1 Bluff, composite Carmel Formation and Entrada Sandstone measured in SW1/4 sec. 29 Monticello to Harts Draw, Cretaceous rocks conceal the Morrison Formation. mi northwest of Moab. Near Monticello, the Dewey Bridge Member consists mainly of dark- The Westwater Canyon Member overlies the Recapture Member along Recapture and SE1/4, sec. 30, T. 40 S., R. 21 E.; Wanakah Formation measured in In the study area, two unconformities are associated with the rocks described herein. reddish-brown siltstone and sandy siltstone, parts of which tend to form spheroidal- WANAKAH FORMATION BLUFF SANDSTONE MEMBER Creek and overlies the Salt Wash Member in the southern part of Montezuma Canyon. The REFERENCES CITED SW1/4 sec. 19 and NW1/4 sec. 30, T. 40 S., R. 22 E.; Bluff Sandstone One at the base of the San Rafael Group (termed J-2) at the contact with the Lower Jurassic weathering features known as hoodoos, stone babies, or goblins.