Magnetic polarity measurements from a well dated (15.6--13.7 Ma) volcanic section in southern Nevada allow resolution of controversies in the calibration of the Middle Miocene polarity time scale. A sequence of lavas yielding exclusively reversed polarities dated at 15.5--14.9 Ma can be confidently identified as C5Br, and the C5Cn.ln(y) reversal is bracketed between 15.67 and 15.48 Ma (relative to TC = 27.92 Ma). Integration with other recent studies shows that polarity chrons C5Cr--C5ABr are now confidently correlated with lava flows dated from 16.9 to 13.4 Ma by the 40Ar/39Ar method.