The shoreline of Puget Sound is rimmed by slopes and steep bluffs that range from five to several hundred feet high. Looking at the bluff faces, you can often see many layers of sand, silt, gravel and clay, which were deposited during the glacial and interglacial periods. As these bluffs erode, they provide the building materials that make up our beaches. Whether the cause is from slide activity or wave action, the sediment falls off the bluffs, where it is carried along the shoreline by wave and wind action. These are often referred to as feeder bluffs, and can feed miles of beaches, creating shore forms such as spits and barrier beaches.
Specific compositions of sand and gravel along a beach are important to many species of marine life. Surf smelt, a forage fish, lay their eggs in the high intertidal zone, in fine gravel and sand substrate. Sand lance, or candlefish, another important forage fish, spawn in shallow water at high tide on sand-gravel beaches, or sometimes on sand beaches. Forage fish are important food sources for salmon, seabirds and other marine species.
Sand and mud beaches support eelgrass beds, which are important habitats for small fish and other marine organisms. Pacific herring, an important forage fish, deposit their eggs on eelgrass blades. Larger fish like salmon depend on healthy eelgrass beds for their survival, as do Dungeness crabs, seabirds, and several other marine species.