The temporal evolution of the ionospheric density enhancement produced by a wide-spread REP has been observed with the Chatanika Radar. The REP was associated with a substorm particle energization event, and both the ionospheric absorption and density perturbation exhibited a ~90 min periodicity associated with the particles' longitudinal drift. A 80 keV characteristic energy for the precipitating electrons is deduced from ground-based and satellite data. At the maximum of the event, electrons deposited ~50 ergs/cm2 sec in the ionosphere, producing a peak density of 5¿105 cm-3 at 89 km altitude. At that time the radar observed densities greater than 105 cm-1 between 70 km and 110 km altitude and riometer absorption at 30 MHz was ~12 db.