Evidence from terrace sequences in southwestern Alberta shows that overbank deposition rather than lateral accretion was the dominant form of sedimentation during the Holocene. The thin basal gravels along most terrace exposures were deposited by lateral-accretion processes similar to those operating within present-day channels and flood plains. The thicker, overlying sediments are fine grained and were produced mainly by overbank deposition from high-discharge events. A less erosive overbank environment for the latter is supported by the presence of undisturbed tephra and archaeological cultural horizons. The overbank deposition appears to have resulted from the combined effects of intense rainfall and fire denudation of forested slopes.