Bluff heights range from 10-50m above lake level and consist of Pleistocene till . It is formed from deposition of sediment directly from melting ice. Studies have shown that the bluffs near Sterling are eroding at rapid rates, cutting back as rapidly as 0.5-1 meter per year. Sediment derived from bluff erosion provides the main input of sediment to the shallow lake waters, beaches, and barrier bars. During the spring, rains generate surface runoff that becomes channelized into rills and gullies, and erosion by running water occurs.
Sediment is moved down rills and gullies and deposited on the beach as fan-shaped deposits.
Persistent rain may saturate the till, causing it to lose its cohesiveness and begin to move as slumps or mudflows. In the summer or other drier periods, the clay-rich bluff tills become very hard. Erosion during these periods is difficult because the till is so cohesive. During the winter, storms generate large waves. However, a build-up of ice at the base of the bluffs forms that protects the bluff face against wave attack.