Named for the giant redwood trees that used to line its banks, the Big River drains a 181.1 square mile watershed located in the northern California Coast Range in western Mendocino County, entering the Pacific Ocean at the town of Mendocino, about 10 miles south of Fort Bragg. The Big River Basin extends 24 miles to the east, to within three miles of Willits and Highway 101. It drains primarily from east to west, sharing ridges with the Noyo River and Caspar Creek basins to the north and the Albion and Navarro river basins to the south. Elevations within the Big River Basin range from sea level at the basin outlet to Irene Peak at 2,836 feet, 5 miles south-southwest of Willits in the east end of the Martin Creek Planning Watershed, Inland Subbasin.
The basin’s topography is diverse along its length, varying from flat estuarine environments and uplifted marine terraces to rugged mountains with high relief in the eastern portion. It is characterized by narrow ridgelines separated by deeply incised inner gorges of the major river channels and streams draining the watershed.
The western end of the drainage is distinguished by a long estuary laden with mudflats that become narrow floodplains further upriver and occupy a relatively narrow inner gorge. A sand bar at the mouth partially restricts the connection to the sea at low flow periods. Tidal influence extends upward from the mouth three miles in the winter and as far as eight miles during the highest spring tides making the Big River Estuary one of the longest estuaries in northern California (Warrick and Wilcox 1981). Inland areas of the basin are characterized by second growth forest, with some grasslands in the southeast margins. Logging of the basin started in the 1860s near the mouth and gradually moved eastward. Early logging included heavy use of splash dams, effects of which can still be seen today. Most of the basin is currently owned by large timber companies and managed for timber harvest, though the state owns some sections, and there are smaller ownships as well.
The Big River is listed on the National Rivers Inventory, a list of potential wild, scenic, and recreational river areas within the United States. The river is listed for five outstandingly remarkable values: scenery, recreation, fish, wildlife, and history (NPS 2004).
The basin supports runs of coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss). Chinook salmon (O. tshawytscha) have been reported occasionally, but there is no significant run. Historical accounts indicate that salmon were plentiful and that salmon fishing was a common activity. However, agency reports starting in the 1950s indicate that salmonid populations were depleted and in decline. In recent years, efforts have been underway to recover salmonid stocks of the Big River Basin. For example, local residents and conservation groups recently organized and purchased a 7,342-acre parcel at the mouth of Big River from a timber company and gave it to California Department of Parks and Recreation to be managed for conservation and recreation.