In addition, wetlands provide a unique opportunity for nature study. Most of California's coastal wetlands are estuarine salt marshes with associated tidal channels and mudflats. Estuaries are formed where freshwater streams meet the sea, and contain variably brackish water. Salt marshes develop along the shores of protected estuarine bays and river mouths, as well as in more marine-dominated bays and lagoons. Wetlands that are less common along the California coast are freshwater marshes, riparian wetlands, bogs, and vernal pools.
Freshwater marshes occur in ponds and slow moving streams.
Like salt water marshes, they are vegetated mostly with herbaceous plants, predominantly cattails, and species of sedges, and rushes. Freshwater marshes have mineral soils that are less fertile than those of salt marshes, and exhibit a greater variety of plant species than do salt marshes. Riparian wetlands, which occur on the banks of steams, rivers, and lakes, commonly feature woody vegetation such as red alder, wax myrtle, and willow. Bogs, unlike marshes and streams, have detrital soils composed of peat, and are vegetated mostly with mosses. Vernal pools occur in small depressions underlain by dense, impenetrable claypan soils that allow water to accumulate in winter and spring.