Palaeomagnetic polarity to the base of the Mammoth subchron (3.15 Myr) has been determined in a core of lacustrine sediments from ancient Searles Lake. The magnetostratigraphy provides a chronological framework for palynological, tephrochronological and palaeoecological studies of the core. Five zones of inclination are found that are not in the polarity time scale of Mankinen and Dalrymple. Three of the zones may correlate with K-Ar-dated lava flows of that polarity elsewhere, and the other two may be new discoveries. ?? 1980 Nature Publishing Group.