Arcata is a city adjacent to the Arcata Bay (northern) portion of Humboldt Bay in Humboldt County, California, United States. At the 2020 census, Arcata's population was 18,857. Arcata was first founded in 1850 as Union, was officially established in 1858, and was renamed Arcata in 1860. It is located 280 miles (450 km) north of San Francisco, and is home to California State Polytechnic University, Humboldt. Arcata is also the location of the Arcata Field Office of the Federal Bureau of Land Management, which is responsible for the administration of natural resources, lands and mineral programs, including the Headwaters Forest, on approximately 200,000 acres (810 km2) of public land in Northwestern California.

Humboldt Bay is a natural bay and a multi-basin, bar-built coastal lagoon located on the rugged North Coast of California, entirely within Humboldt County, United States. It is the largest protected body of water on the West Coast between San Francisco Bay and Puget Sound, the second-largest enclosed bay in California, and the largest port between San Francisco and Coos Bay, Oregon. The largest city adjoining the bay is Eureka, the regional center and county seat of Humboldt County, followed by the city of Arcata. These primary cities, together with adjoining unincorporated communities and several small towns, comprise a Humboldt Bay Area with a total population of nearly 80,000 people. This comprises nearly 60% of the population of Humboldt County. The bay is home to more than 100 plant species, 300 invertebrate species, 100 fish species, and 200 bird species. In addition, the bay and its complex system of marshes and grasses support hundreds of thousands of migrating and local shore birds. Commercially, this second-largest estuary in California is the site of the largest oyster production operations on the West Coast, producing more than half of all oysters farmed in California.