Teeth collected from Pleistocene surficial sediments in southeastern Alberta and western Saskatchewan have been dated by electron spin resonance (ESR). The dates generally agree with the previously determined temporal sequence of the deposits, largely based on studies of fossil vertebrates and supplemented by some absolute ages, but the absolute ages of the oldest deposits appear to be much younger than previously estimated. Absolute ages (ESR) have been compared with faunal ages (using nomenclature of Stalker and Churcher): the age of Aftonian – early Kansan deposits at the Maser–Frisch site is 450 ± 30 ka; Kansan deposits in the Medicine Hat region range from 410 to 250 ka; Sangamon deposits at Mitchell Bluff are 67 ± 12 ka; middle Wisconsinan deposits at Empress, Alberta, are 34 ± 4 ka; postglacial beds near Medicine Hat give ages of 11 ± 2 ka (in agreement with 14C ages). At Wellsch Valley, however, ESR dates (280 ± 35 ka) are much younger than the age of about 1.5 Ma obtained from fauna, fission track, and paleomagnetics. This discrepancy may be due to late introduction of U into the teeth.