The age of the basement of the northern sector of the Powell Basin has been determined, using multichannel seismic reflection profiles, magnetic data, and heat flow measurements. Seismic data show that the northern sector of the Powell Basin is floored by oceanic crust, and presents a well preserved fossil ridge axis. Along three magnetic profiles crossing the ridge axis, oceanic-related magnetic anomalies were identified and interpreted. The analysis indicates that in the northern sector of the Powell Basin, sea floor spreading started at about 28 Ma and almost stopped at approximately 17 Ma. From 17 Ma to about 4 Ma, spreading activity was greatly reduced. The age-depth law has been applied to the oceanic basement, interpreted along a seismic profile, after correction for sediment loading and flexural effects in order to asses its age. Published heat flow data have been reinterpreted, and combined with the magnetic and seismic data. A new map of Chrons for the northern sector of the Powell Basin has been produced, and a tentative sketch for its tectonic development has been outlined.