Integrated geology and preliminary cross section along the north ramp of the Exploratory Studies Facility, Yucca Mountain

The Exploratory Studies Facility is a major part of the site characterization activities at Yucca Mountain, Nevada, and the north ramp is the first phase of construction. The N61W trending north ramp will transect the Bow Ridge and Drill Hole Wash faults and numerous minor faults, and traverses two thick welded tuffs and several nonwelded tuff units. A preliminary cross section along the north ramp was created by integration of geologic map relations, lithostratigraphic data from core collected from boreholes, and surface and borehole geophysical data. The Bow Ridge fault is a west-dipping normal fault with about 410 feet of dip-slip separation. East-dipping strata in the hanging wall adjacent to the fault is contrary to early structural interpretations. West of the Bow Ridge fault the ramp might traverse about 220??65 feet of nonlithified tuffaceous material. Geometry of the Drill Hole Wash fault is not known, but is modeled in part as two strands that juxtapose different thicknesses and facies of formations with a complex sense of movement.