Humboldt Lagoons State Park is a state park located in northern California. The state park includes access from U.S. Route 101 to three lagoons on the Pacific coast between Eureka, California and the Oregon border. Big Lagoon is the largest and southernmost lagoon. Stone Lagoon is the middle lagoon; and Freshwater Lagoon is the northernmost and smallest lagoon. 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. Studies around Humboldt Bay indicate tectonic activity along the Cascadia subduction zone has caused local sea level changes at intervals of several centuries. The alluvial plain forming each shallow lagoon may support fresh water wetlands or Sitka Spruce forests following uplift events and salt marsh or inundated shellfish beds following subsidence events.