New 1:24,000-scale geologic mapping in the Storm King Mountain7.5' quadrangle, in support of the USGS Western Colorado I-70Corridor Cooperative Geologic Mapping Project, provides new dataon the structure on the south margin of the White River upliftand the Grand Hogback and on the nature, history, anddistribution of surficial geologic units.Rocks ranging from Holocene to Proterozoic in age are shown onthe map. The Canyon Creek Conglomerate, a unit presently knownto only occur in this quadrangle, is interpreted to have beendeposited in a very steep sided local basin formed bydissolution of Pennsylvanian evaporite late in Tertiary time.At the top of the Late Cretaceous Williams Fork Formation is aunit of sandstone, siltstone, and claystone from which LateCretaceous palynomorphs were obtained in one locality. Thisinterval has been mapped previously as Ohio Creek Conglomerate,but it does not fit the current interpretation of the origin ofthe Ohio Creek. Rocks previously mapped as Frontier Sandstoneand Mowry Shale are here mapped as the lower member of theMancos Shale and contain beds equivalent to the Juana LopezMember of the Mancos Shale in northwestern New Mexico. ThePennsylvanian Eagle Valley Formation in this quadrangle gradesinto Eagle Valley Evaporite as mapped by Kirkham and others(1997) in the Glenwood Springs area.The Storm King Mountain quadrangle spans the south margin of theWhite River uplift and crosses the Grand Hogback monocline intothe Piceance basin. Nearly flat lying Mississippian throughCambrian sedimentary rocks capping the White River uplift arebent into gentle south dips and broken by faults at the edge ofthe uplift. South of these faults the beds dip moderately tosteeply to the south and are locally overturned. These dips areinterrupted by a structural terrace on which are superposednumerous gentle minor folds and faults. This terrace has aneast-west extent similar to that of the Canyon CreekConglomerate to the north. We interpret that the terrace formedby movement of Eagle Evaporite from below in response todissolution and diapirism in the area underlain by theconglomerate. A low-angle normal fault dipping gently northnear the north margin of the quadrangle may have formed also inresponse to diapirism and dissolution in the area of the CanyonCreek Conglomerate. Along the east edge of the quadrangleMiocene basalt flows are offset by faults along bedding planesin underlying south-dipping Cretaceous rocks, probably becauseof diapiric movement of evaporite into the Cattle Creekanticline (Kirkham and Widmann, 1997).Steep topography and weak rocks combine to produce a variety ofgeologic hazards in the quadrangle.
