The only formal morphostratigraphic units recognized in IL are units related to moraines that are called "drifts." Is named for Ridge Farm, Vermilion Co, IL (Illinois basin); is based on the Ridge Farm Moraine (mapped on pl. 1) and was previously called the Middle Champaign Moraine in the Danville region (Eveland, 1952). It is a well-defined ridge extending about 25 mi from its contact with the Urbana Moraine to the IL-IN state line. It is 1 to 2 mi wide and its crest has a maximum height of 30 to 40 ft above the valley along its front. Several isolated patches of morainic topography behind the moraine may represent a temporary stand during retreat of the ice but are included in the Ridge Farm Moraine. Although the Ridge Farm and Hildreth Drifts may be a continuation of the Champaign Drift east of the area where it is overlapped by the Urbana Moraine, evidence of continuity is lacking and separate names seem preferable. Deposited by the Decatur Sublobe of the Erie Lobe. Assigned to Woodfordian Substage of Wisconsinan Stage in Pleistocene Series.

Source: GNU records (USGS DDS-6; Denver GNULEX).