Recent evidence based on ages of large landslides and the existence of severely disturbed terrain in Champlain Sea sediments to the east of Ottawa suggests that this area may have been the site of two of the most geologically destructive earthquakes in eastern Canada. The walls of several paleochannels, downcut into sensitive marine clayey silts, are scarred by numerous large earthflows of sizes unequaled in historical time. While radiocarbon ages of 15 landslides, as much as 35 km apart, range from ca. 1870 to 5130 yr B.P., the majority of events cluster at ca. 4550 yr B.P. The coincidence of numerous large failures in different paleovalleys, occurring concurrently, long after channel abandonment and at a time of drier climate, suggests that the widespread landsliding was triggered by a strong earthquake. Close to the landslide area, areas of very disturbed terrain in a flat erosional plain show severely deformed bedding and irregular ground subsidence and are attributed to a large earthquake, ca. 7060 yr B.P., that strongly shook a thick sequence of sensitive material filling deep, steep-sided, bedrock basins.