Big River flows for 42 miles (68 km) through the northern California Coast Range, beginning at an elevation of about 2,800 feet (865 m) and drains a watershed covering 181 square miles (46,880 ha) before emptying into the Pacific Ocean at Mendocino, California. The estuary extends 8.3 miles (13.4 km) upstream from the river mouth in summer and 3 miles (5 km) in winter when the river discharge is highest.

The Big River watershed was historically inhabited by the Me-tum’mah, or Mitom Pomo tribe. Named for the giant redwoods that once lined its banks, Big River appeared as Arroyo Grande on maps of the original Albion Mexican land grant dated October 30, 1844. The timber industry has dominated the area since the 1850s, and logging practices severely impacted the estuary. The first mill was constructed in Mendocino City on the bluffs overlooking the river mouth and the estuary served as a millpond from 1852 to 1938. An apron chute was built to load lumber onto schooners anchored in the estuary. Splash dams were constructed on the river, and their floodgates were opened each winter to sweep logs downstream to booms that prevented the logs from floating out to sea. This method of log transport increased erosion, removed woody debris, and buried cobble substrates.

In 1980, the U.S. Fish and Wildlife Service nominated the Big River estuary for protection under the Unique and Nationally Significant Wildlife Ecosystem Program but was not granted the status. The estuary gained protection in 2002 when the Mendocino Land Trust purchased a 7,334-acre (2,968-ha) parcel from the Hawthorne Timber Company. This land was donated to California State Parks as part of the Mendocino Headlands. In 2010, the estuary waters were designated as a State Marine Conservation Area under the Marine Life Protection Act. Today, the Big River Estuary State Marine Conservation Area is a small marine protected area located just south of the town of Mendocino. It covers less than a quarter square mile of estuary habitat along 1.3 miles (2.1 km) of riverbank, east of the Highway 1 bridge. Big River Beach offers access for launching canoes and kayaks onto the protected waters of the Big River Estuary. Read more here and here. Explore more of Big River and Mendocino here: