The Sac River has created a cut bank, some 5.2 meters high, revealing a rare site similar to the Rodgers Formation of the neighboring Pomme de Terre valley (Lopinot et al. 1998:39-40). Haynes (1976:58-59) describes the deposits in the area of Rodgers Cave as flood plain deposits which have accumulated slowly through annual flooding. Periodically, the river would downcut deeply enough to prevent further flooding, only to change its course later and restart the process. This leaves a series of easily identified layers, separated by periods of no deposits. Big Eddy was formed in a similar way. For some 14,000 years, the Sac River has gently flooded, covering over this site with thick, well stratified, alluvial silt (Bush 2006).