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

water deposits of Cenomanian age (Nichols, 1997); based on map measurements,about 1300 to 1400 feet (400-425 m) thick at the south end of Jones Hill west ofMaple Canyon.KiKcmIron Springs Formation, undivided (Upper Cretaceous, Santonian or lowerCampanian to Cenomanian) – Interbedded, ledge-forming, calcareous, crossbedded,fine- to medium-grained sandstone and less-resistant, poorly exposedsandstone, siltstone, and mudstone present in the Red Hills at the west edge of themap area; the formation is variously colored grayish orange, pale yellowishorange, dark yellowish orange, white, pale reddish brown, and greenish gray andis locally stained by iron-manganese oxides; Liesegang banding is common in thesandstone beds; sandstone beds range from quartz arenite to litharenite (Fillmore,1991; Goldstrand, 1992); the entire formation weathers to repetitive, thick tabularsandstone beds and thinner interbedded mudstone; lower part (in the upper plateof the Iron Springs thrust) contains numerous oyster coquina beds commonly 1 to3 feet (0.3-1 m) thick; upper contact with the upper conglomerate of the GrandCastle Formation is difficult to map on the east and south sides of the Red Hillsdue to abundant TKgcu-derived colluvium and faults; deposited principally inbraided-stream and floodplain environments of a coastal plain (Johnson, 1984;Fillmore, 1991; Eaton and others, 2001; Milner and others, 2006); mapped in theRed Hills where it is correlated to the Dakota Formation, Tropic Shale, andStraight Cliffs Formation (Eaton, 1999; Eaton and others, 2001); age fromGoldstrand (1994) and an ash that is 712 feet (217 m) below the top of theformation in Parowan Canyon (here reassigned to the upper part of the StraightCliffs Formation), which yielded an 40 Ar/ 39 Ar age of 83.0 ± 1.1 Ma (Eaton andothers, 1999b); lower Iron Springs strata (in the upper plate of the Iron Springsthrust) may be associated with the maximum transgression of the Greenhorn Seaof late Cenomanian or early Turonian age (Eaton and others, 1997; Eaton, 1999);Milner and others (2006) reported on dinosaur tracks in upper Iron Springs stratanear Parowan Gap, and also noted a diverse assemblage of plant fossils, bivalves,gastropods, turtles, fish, and trace fossils suggestive of upper Santonian to earlyCampanian age (Milner and Spears [2007] mistakenly reported an early Turonianage for these same beds); incomplete sections are about 2500 feet (750 m) thick inthe Red Hills (Maldonado and Williams, 1993a) and about 1100 feet (335 m)thick in Parowan Canyon (Maldonado and Moore, 1995), but the entire formationis about 3500 to 4000 feet (1070-1220 m) thick in the Pine Valley Mountains(Cook, 1960).Cedar Mountain Formation (Cretaceous, Cenomanian to Albian) − Consists ofa basal pebble conglomerate overlain by brightly colored variegated mudstone inCedar Canyon. Mudstone is variegated gray, purplish-red, and reddish-brown,distinctly different from the gray and yellowish-brown hues of overlying Dakotastrata; clay is smectitic and weathers to “popcorn-like” soils; includes minor lightgrayto dark-yellowish-brown, fine- to medium-grained channel sandstone. Basalconglomerate is grayish brown and typically poorly cemented and non-resistant;clasts are subrounded to rounded, pebble- to small-cobble-size quartzite, chert,60