Strike-slip faults in the Basin and Range province have often been considered passive boundaries between differentially extended domains of tilted normal faults and are thus considered secondary in accommodating regional horizontal deformation. Paleomagnotic investigation of late Miocene age volcanic rocks, displaced by the left-lateral fault system of Lake Mead, Nevada, shows: (1) that these rocks have not been affected by significant structural tilt, the difference between observed and expected inclinations being only −0.6° ± 14.9° and (2) a significant horizontal counterclockwise rotation of −29.4° ± 8.5° about a vertical axis. This rotation was accommodated by slip on northwest-trending, right-lateral strike-slip faults; this implies significant west-northwest elongation. Results of the investigation indicate that strike-slip faulting is the primary process accommodating crustal deformation along the Lake Mead fault system and that tilting in response to normal faulting is secondary.

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