Big Lagoon (California)

Big Lagoon
Kayaks at the south end of Big Lagoon
Location	Humboldt County, California
Coordinates	41°11′00″N 124°07′00″W / 41.18333°N 124.11667°W / 41.18333; -124.11667
Type	Lagoon
Primary inflows	Maple Creek
Primary outflows	Pacific Ocean
Basin countries	United States
Max. length	3.8 mi (6 km)
Max. width	1.4 mi (2 km)
Surface area	1,470 acres (5.9 km2)
Max. depth	22 feet (6.7 m)
Shore length1	9 miles (14 km)
Surface elevation	20 feet (6.1 m)
Frozen	No
1 Shore length is not a well-defined measure.

Big Lagoon is the southernmost and largest of three similar lagoons within Humboldt Lagoons State Park, along the coast of Humboldt County, California.

It is located between Trinidad to the south and Orick at the mouth of Redwood Creek to the north.

The lagoons are shallow bays between rocky headlands where coastal wave action has formed a sandy bar separating each lagoon from the Pacific Ocean. The lagoons are resting areas for migratory waterfowl using the Pacific Flyway between Lake Earl on the Smith River estuarine wetlands 40 miles (70 kilometers) to the north and Humboldt Bay on the Mad River estuarine wetlands 30 miles (50 kilometers) to the south.

Big Lagoon is similar to other coastal features of northern California including Humboldt Bay to the south and Lake Earl to the north. An alluvial plain is surrounded by steep uplands. Hills adjacent to Big Lagoon have been identified as the Franciscan Assemblage along the eastern shore and dune sandstone to the south. Studies around Humboldt Bay indicate tectonic activity along the Cascadia subduction zone has caused local sea level changes at intervals of several centuries. The plain may support fresh water wetlands or Sitka Spruce forests following uplift events and salt marsh or inundated shellfish beds following subsidence events. At the present lagoon level, the sand bar normally separates the lagoon from the ocean during summer months. Winter precipitation may raise the water level in the lagoon a few meters above sea level. Hydrostatic pressure and storm surf may then breach the sand bar allowing the lagoon to drain into the sea and then receive tidal inflow until wave action reforms the bar.