Ahjumawi Lava Springs State Park, State park in Shasta County, California, United States

Ahjumawi Lava Springs State Park is a 5,930-acre protected area in Shasta County, California, reachable only by boat. It measures 4 miles long and at most 1 mile wide, with over 13 miles of shoreline along the Fall River, creeks, and Big Lake. About two-thirds of the park is covered by jagged black basalt from lava flows of the last two to five thousand years.

Pacific Gas & Electric owned large tracts of the swampland, and a muskrat farm operated there until the 1930s. The state of California acquired the land from private owners in 1975. Big Lake, along much of the shoreline, was created when levees and canals were installed.

The name Ahjumawi comes from the Achomawi people, one of the Pit River Tribe bands, who constructed stone fish traps along the shoreline that remain visible today. These structures show how the original inhabitants worked with the waterways.

There are no public roads into the park and private motor vehicles are prohibited inside it. Boats can be launched into Big Lake at the PG&E public boat launch known as Rat Farm; from there visitors reach three basic campsites and about 20 miles of hiking trails. Canoes and kayaks can travel the narrow waterways. Fishing is allowed, hunting is not.

The park sits on one of the nation's largest systems of underwater springs, which release about 1.2 billion US gallons (4.5 billion litres) of fresh water daily. That water begins as snowmelt on the Medicine Lake Volcano highlands. The springs feed the Fall River and the creeks and lakes within the park.