Seismic-reflection and borehole data along with crustal-scale refraction/reflection data provide new evidence for the Cenozoic tectonic evolution of the Ruby Mountains metamorphic core complex and Huntington, Ruby, and Lamoille valleys. Analyses of these data suggest: (1) along the western flank of the Ruby Mountains an early stage of upper-crustal extension provided accommodation space for deposition of apparently synextensional strata; (2) the oldest sedimentary rocks in the developing basin along the western flank of the Ruby Mountains are middle Eocene in age, suggesting that active upper-crustal extension and early basin formation in northeastern Nevada began at least by that time; (3) Ruby Valley is bounded by high-angle, east-dipping normal faults on the west and a relatively low-angle, west-dipping normal fault on the east; (4) crustal thicknesses beneath the eastern flank of the Ruby Mountains do not reflect local topographic relief and estimated amounts of extension; and (5) adjacent to the range, maximum thicknesses of basin-fill sedimentary rocks do not directly reflect maximum amounts of exhumation of the Ruby Mountains. Together, these observations suggest that either preexisting crustal roots (subsequently dissipated), or middle- or lower-crustal flow prior to and during extension, were involved in evolution of the core complex.

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