DETERMINING THE NATURE OF THE CONTACT BETWEEN THE EASTERN SIERRA NEVADA MOUNTAIN FRONT AND THE BIG PINE VOLCANIC FIELD SOUTH OF GOODALE CREEK IN OWENS VALLEY, CALIFORNIA

The Sierra Nevada Frontal Fault Zone (SNFFZ) located along the western boundary of Owens Valley is comprised of numerous Quaternary normal faults. These faults generally are assumed to dip 60° and long-term extension rates for Owens Valley are calculated assuming these steep dips. Recent studies conducted in the Independence and Lone Pine areas of Owens Valley and farther north in the Bishop area show shallow dips of 26-52°. These shallow dips affect long-term extension rate calculations and the kinematic history of Owens Valley. Quaternary Big Pine Volcanic field (BPV) basalt deposits that crop out along the mountain front offer an opportunity to evaluate potential SNFFZ fault orientations in this area. This study analyzes the contact between the mostly granitic rocks of the Sierra Nevada Mountains and the BPV in the vicinity of Aberdeen from just south of Sawmill Creek and north to Goodale Creek. Working hypotheses for this contact include: (1) it is a depositional contact along the mountain front and (2) it is a fault contact. These hypotheses are tested by mapping the contact and surrounding rocks in detail. GPS locations of the contact were taken where the contact is clear. In general, the basalt-granite contact trends NNW, however north of Sawmill Creek the contact steps west consistent with the mountain front and the faults of the SNFFZ. Locally, especially south of Sawmill Creek, the basalt deposits are present on ridges with granitic basement in the intervening valleys so that the contact V’s to show an eastward dip, consistent with east-dipping fault contact. Preliminary 3-point calculations along the contact suggest the contact dips about 25° E. In other areas the contact is diffuse with thin scoria deposits located uphill from the presumed location of the frontal fault. The mapping is being correlated to detailed Google Earth images to better define the relationships between basalt exposure and fault locations. Where the contact can be clearly defined, plane-fitting analysis using GPS- and Google Earth-derived x,y,z locations may refine potential fault orientations. This work will lead to a better understanding of the relationships between the BPV distribution and SNFFZ faults and may help constrain the SNFFZ orientation for kinematic analysis.