The geologic history of the surficial units of the Bethany Beach and Assawoman Bay Quadrangles is that of deposition of the Beaverdam Formation and its subsequent modification by erosion and deposition related to sea-level fluctuations during the Pleistocene. The geology reflects this complex history onshore, in Indian River Bay and Assawoman Bay, and offshore in the Atlantic Ocean.

In the period between January 27 and February 6, 1998, the Mid-Atlantic region experienced two significant northeasters that affected the coast of Delaware and Maryland. These storms produced heavy rains and high winds, waves, and tides that created dune washovers, flooding, wind damage, and beach erosion and migration. Coastal communities were impacted by flooding that closed roads, by beach erosion that affected structures, streets and boardwalks, and by high winds that damaged structures and trees.