The Geology of Coos Bay by Kenn Oberrecht Geology is the science concerned with the physical history and dynamics of earth. It's not only a study of the rocks and sediments that form our planet, but also of past and present physical, biological, and chemical processes that have shaped and reshaped earth and continue to do so. The major geologic processes in Coos Bay include the tidal movement of salt water, the inflow of fresh water, water mixing, and sedimentation.
Winds also erode dunes and blow loose sand into the bay.
Deposition of sediments in Coos Bay has created shoals, tidal flats, and tidal marshes. Bottom material of the upper bay is mainly silt, fine sand, and mud. Downbay, the bottom is predominantly sand and shell fragments. Sand is abundant in the main channel. Just over half of Coos Bay's 12,380 acres consist of tidal flats.