We propose that hummocky terrain in south-central Alberta is the product of subglacial erosion rather than supraglacial letdown during ice disintegration (a common view of hummock formation). Extensive exposures in hummocks contain sediments marking the history of Laurentide ice advance and deglaciation in the region. Regardless of the genesis of those sediments, units are abruptly truncated at the surface that represents the hummock and trough morphology, indicating that the hummocks are the product of differential erosion. Subglacial sediments predating the erosion and subglacial eskers overlying the erosion surface suggest that the erosion was also subglacial. Hummock morphology, lithostratigraphy correlated from hummock to hummock, truncation at the land surface, and widespread coarse boulder lags support a glaciofluvial origin for hummocky terrain in this region.