Interim Geologic Map of the West Part of - Utah Geological Survey

interval, and a lower limestone interval) and the lower red member. This map is the firstpublication with the several lithologic facies of the white member of the Claron mappedseparately, which has proven useful to better understand faulting at the west edge of theMarkagunt Plateau, the distribution of overlying volcaniclastic units of the Brian Headand Limerock Canyon Formations, and the southern depositional limit of the Markaguntmegabreccia and location of inferred toe thrusts. The Claron Formation consists ofmudstone, siltstone, sandstone, limestone, and minor conglomerate deposited in fluvial,floodplain, and lacustrine environments of an intermontaine basin bounded by Laramideuplifts (Schneider, 1967; Goldstrand, 1990, 1991, 1992; Taylor, 1993; Ott, 1999). Muchof the red member, and clastic parts of the white member, were greatly modified bybioturbation and pedogenic processes, creating a stacked series of paleosols (Mullett andothers, 1988a, b; Mullett, 1989; Mullett and Wells, 1990; see also Bown and others,1997). The Claron Formation is typically forested and covered by colluvium, but it formsthe Pink Cliffs, the uppermost riser of the Grand Staircase, and is spectacularly exposedat Cedar Breaks National Monument and Bryce Canyon National Park. It is mostlynonfossiliferous and its age is poorly constrained as Eocene to Paleocene (Goldstrand,1994; Feist and others, 1997).Tcw White member, undivided (Eocene) – Used for areas south of Blue SpringMountain and west of the Brian Head resort where incomplete and isolatedexposures preclude subdivision; query indicates uncertain correlation in thenorthwest corner of the Brian Head quadrangle. The entire white member isabout 340 feet (100 m) thick in Rock Canyon; Hatfield and others (2003) reportedthat it is 360 feet (110 m) thick at Cedar Breaks National Monument, but if thelower sandstone and conglomerate unit of Sable and Maldonado (1997b) isincluded as part of the white member, as suggested here, the thickness is 440 feet(135 m) (regardless, the white member is truncated south of Cedar BreaksNational Monument by late Tertiary and Quaternary erosion associated withdevelopment of the Markagunt Plateau); Moore and others (1994) reportedsignificant facies changes in the white member in the Asay Bench quadrangle, butthere, in aggregate, it is 448 feet (137 m) thick. Sinkholes are common in thewhite member in the central Markagunt Plateau (Hatfield and others, 2003; Mooreand others, 2004; Biek and others, 2007; Rowley and others, in preparation); largesinkholes visible on 1:20,000-scale aerial photographs are plotted on the geologicmap, and doubtless many smaller sinkholes are present; these sinkholes capturelocal runoff and serve to shunt shallow ground water rapidly down dip where itemerges as springs, including the large Mammoth and Asay Springs (Wilson andThomas, 1964; Spangler, in preparation).Tcwt Uppermost mudstone, siltstone, and sandstone interval of white member(upper and middle Eocene) – Varicolored and commonly mottled, pale-reddishorange,reddish-brown, moderate-orange-pink, dark-yellowish-orange, grayishpink,and similarly hued calcareous mudstone and siltstone, locally with minorfine-grained silty sandstone and micritic limestone; indistinguishable in lithologyand color from the middle white (Tcwm) and red members (Tcr) of the ClaronFormation; forms a brightly colored slope on top of the upper white member ofthe Claron Formation in the northern part of Cedar Breaks National Monument46