In humid environments surface water erosion, rather than seepage water erosion has been considered the major erosional force. The canyons in Starved Rock State Park, north-central Illinois, are not typical in form for eastern United States humid-temperate climate landscapes. In and around Starved Rock State Park the valley cross-profiles are box shaped rather than "V"-shaped with amphitheater heads, steep walls and broad valley bottoms. Other large and small-scale features of the canyons are also largely indicative of seepage erosion.Using field data it was determined that active canyon headwall erosion was occurring in the park at a rate of approximately 0.02 m/year. This is in fact the rate that would be needed to erode the canyons to their current length, showing that seepage erosion, the dominant erosional force in the park, is indeed capable of erosion rates necessary to entirely form the canyons within Starved Rock State Park. / Department of Geology