According to the
United States Census Bureau, Humboldt County encompasses , of which is land and is water.
Cape Mendocino is the westernmost point in California (
longitude 124 degrees, 24 minutes, 30 seconds).
Humboldt Bay, the only deepwater port between San Francisco and
Coos Bay, Oregon, is located on the coast at the midpoint of the county. Humboldt County contains a diversity of plant and animal species, with significant forest and coastal habitats. In coastal areas there are extensive
redwood forests. A prominent understory shrub is the
toyon, whose northern range limit is in Humboldt County.
Rivers on the Pacific Coast , the largest remaining old-growth
Redwood forest on earth, is located within
Humboldt Redwoods State Park. Humboldt County's major rivers include (in order of flow – in cubic meters per second – from largest to smallest): •
Klamath River •
Eel River •
Trinity River •
Mad River The smaller rivers include Redwood Creek, significant due to amount of its flow; the
Van Duzen; the Eel River syncline group composed of the
South Fork, the
North Fork, and the
Salt River; the
Mattole, Salmon, Elk, Bear, and
Little rivers.
Seismic activity Historically, Humboldt County and the entire far north coast of California have had many earthquakes over 6.0 magnitude. The
Mendocino fracture zone is in the area. The
1992 Cape Mendocino earthquakes were a series of three major earthquakes that occurred off the coast of Cape Mendocino, California on April 25 and 26, 1992, the largest being a 7.2. Ninety-five people were injured and property in the county sustained considerable damage. In 2010, a
6.5 magnitude earthquake struck offshore, west of
Eureka, resulting in only minor injuries and some structural damage to houses and utilities, and no fatalities reported. In 2022, a
6.4 magnitude earthquake centered approximately from Ferndale caused damage, especially in Rio Dell. The
2024 Cape Mendocino earthquake was a Mww 7.0 earthquake with an epicenter off the coast of Humboldt County.
Climate The coastal zone of the county experiences very wet, cool winters and dry, mild foggy summers. In the winter, temperatures range from highs of to lows of . Coastal summers are cool to mild, with average highs of and frequent fog. Coastal summer temperatures range from highs of to lows of . In the populated areas and cities near the coast, the highest temperatures tend to occur at locations just a few miles inland from Eureka and Arcata, in towns like Fortuna, Rio Dell, and smaller unincorporated communities located somewhat further away from Humboldt Bay. In these locations summer highs are . The coastal zone experiences a number of frosty nights in winter and early spring, though snowfall and hard freezes are rare. Coastal winters are cool and wet. Winter rainstorms are frequent, with averages from a year, depending upon elevation. Inland areas of the county also experience wet, cool winters. Snowfall is common at elevations over throughout the winter months, and is deep enough at higher elevations to have inspired the opening of a small ski lift operation (now defunct) on Horse Mountain, near
Willow Creek, for several decades in the late 20th century. Summer displays the sharpest difference between the coastal and inland climates. Inland regions of Humboldt County experience highs of depending on the elevation and distance from the ocean. Occasional summer highs of are common in eastern and southern parts of the county including Orleans, Hoopa, Willow Creek, Garberville, Honeydew, and inland river valleys. ==Demographics==