Relative and absolute elevations of the Sierra Nevada and adjacent Basin and Range province, timing of their differentiation, and location, amount, and timing of strike-slip movement between them are controversial. The provincial boundary near Reno developed in two stages. (1) At ca. 12 Ma, the ≥700 km2 Verdi-Boca sedimentary basin formed across what was to become the boundary, probably as a result of a small-magnitude but regional extensional episode that affected much of the western Basin and Range. (2) At 3 Ma, the basin was complexly faulted and folded during a larger magnitude extensional episode that established the modern Sierran structural and topographic boundary in this area. The boundary is really a transition zone with a western edge along the Donner Pass, California, fault zone, which is farther west than previously placed. Both episodes appear to have resulted from east-west extension only, which suggests that northwest motion of the Sierra Nevada relative to the Basin and Range shown by geodetic data began after 3 Ma or was taken up farther east.