That this rise to the Bonneville level, over?ow, and subsequent drop to the Provo level were concomitant with the maximum of the final Pleistocene glacial period has been, if not established beyond all doubt, generally postulated by geologists.3 In terms of years, this glacial maximum is presumed to have endured from about to years ago.4 A number of thousand years must, however, be allowed for the inaccuracies of such a broad estimate and for the possibility that fluctuations in Lake Bonneville were not precisely correlated with changes in the continental glaciation.