Tips from a local geologist on visiting the Mendocino Coast

Last month, we guided you on a daytrip tour of the Sonoma County coastline, seen through the eyes of a geologist. Now we venture farther north, to the Mendocino County Coast, where the interesting rock formations, unique beaches and natural landmarks continue.

While it sounds odd, to get to the South Coast, you have to drive through the North Coast. That’s because Mendocino County residents refer to the coastal area south of Fort Bragg to Gualala as the South Coast, and the Sonoma County region that runs from Bodega Bay north to the Gualala River is referred to as the North Coast.

Gualala (pronounced “Wah-la-la” by locals, from the original Pomo name) is 6 miles north of The Sea Ranch and just over the Sonoma-Mendocino county line. The unincorporated community offers lodging, camping, groceries, shops and the only bookstore on the coast south of Mendocino (Four-Eyed Frog Books in the Cypress Village shopping center).

The Redwood Coast Land Conservancy, through an unnamed buyer, is purchasing 112 acres just inside the mouth of the Gualala River, at the south entrance to Gualala. The land includes an estuary, wetlands and the site of old timber mills once owned by logging companies. The river is accessible, and there are plans for trails along the river and estuary.

The Gualala River basin covers 300 square miles, from Lake Sonoma to the coast. The San Andreas Fault cuts a nearly straight line down the major north and south forks of the Gualala River, then follows the Garcia River to Point Arena.

Five miles north of Gualala is Anchor Bay (Highway 1 postmile marker 4.6), with a small strip of shops and a couple of restaurants (Mexican and Thai). On the north edge of town is a campground at the cove with a marvelous beach area. Although private, it’s accessible to the public for a small fee.

Just 10 miles north is Hearn Gulch, another acquisition held by the Redwood Land Conservancy. This is a must-see scenic-plus-geologic stop. At the boundary of the yellow sandstone of the Galloway Formation and the black rocks of the Iversen Basalt, you’ll find the only igneous rock you will encounter on the “South Coast.” This consists of a series of thin black pillow basalt rocks with white inclusions of a mineral and vesicles (small cavities) of what were previously gas bubbles. At Schooner Gulch (postmile marker 11.35), a fault ends the basalt layer.

Rock spheres, sinkholes

If you can go when the tide is low, visit Bowling Ball Beach, just north of Galloway Creek, as the truly unique “bowling balls” can only be seen at low tide. These round rock balls are an astonishing 3 to 4 feet in diameter and number about 100. They lie in perfect bowling ball “lanes” and consist of sandstone.

How were they formed? Why are they close to each other and in straight lines? And are they eroding out of the bedrock formation or did they get there in some other way? Some people believe the bowling balls were rolled around by the ocean and left in this particular spot. A true geological puzzle!

A mile north at Pelican Beach is Moat Creek (postmile marker 12.89), with the strangest rocks you will encounter in the area. Here there are faults, anticlines and synclines (folds in stratified rock), a mess to understand geologically. Apparently these are deep-water landslide deposits, probably formed at the edge of the Continental Shelf. A storm or an earthquake caused these unstable sediments to slip off the edge of our continent.

Point Arena is 15 miles north of Gualala and has a city government, unlike the unincorporated communities nearby along the coast. It’s an interesting small town populated by people with diverse interests. The library and theater are owned and maintained by local residents. The theater is one of the few places in California where you could watch the Met Opera via live telecast (pre-COVID-19, of course). These taped events are now offered streaming from their homepage, ArenaTheater.org, and are free.

Set on 23 acres, the Point Arena Lighthouse also is owned by locals, and this year they’re celebrating their 150th anniversary with lots of commemorative merchandise available at the Light Station Store as well as their new outdoor museum. Open from 10 a.m. – 3:30 p.m. daily, admission is $5 per person and children under 12 are free. PointArenaLighthouse.com has more information. The historic lighthouse itself is closed due to COVID-19 restrictions, given its tight interior spaces.

Sinkholes like the one that opened up near the lighthouse in early 2019 are caused by waves working in sea caves which capture the overlying material. Sadly, this erosion just east of the lighthouse will continue.

There are numerous walking trails in the Stornetta Public Lands, which are part of the California Coastal National Monument that stretches from Manchester Beach (the largest sand dunes in the area) to Point Arena. Parking and a trail entrance are at the city offices on the north end of Point Arena. Another entrance is at Lighthouse Road at the ocean’s bluff edge (face masks must be worn on the trails).

Arena Cove is the only seaport north of Bodega Bay and south of Fort Bragg, but it’s currently closed for boat launching. The rocks here are miocene shale, sandstone and siltstone. Only recently did I fully appreciate the north wall of the cove. A fault runs down it along the access road. Where the north face has been uplifted, you will notice three black bands of sandstone cutting diagonally down to the west, one up to 17 feet in thickness. Wading into the surf a bit, you can pick up black rocks, which are filled with asphalt! This was once a deposit of oil, but the fault allowed all the lighter hydrocarbons to escape into the atmosphere.

Wild animals

On a private nature farm nearby is the B. Bryan Preserve, where you can visit wild animals from Africa. They’re not a typical zoo but have large herds of giraffes, zebras and antelope, all roaming about in a natural setting spanning 110 acres. Founded by Dr. Frank Mello and his wife, Judy, these longtime wildlife enthusiasts are committed to the breeding and conservation of African hoof stock. Various tours are available, masks are required as are reservations and you can book online. BBryanPreserve.com has more information.

At postmile marker 40.0, Highway 1 crosses the Navarro River and intersects with Highway 128, which can take you inland to Highway 101 toward Santa Rosa and the Bay Area. If you stay north to Mendocino, at postmile marker 50.5 you will arrive at a favorite tourist area with all kinds of shops, restaurants, lodging and gas. Another 10 miles will put you in Fort Bragg, where you can connect on Route 20 to head inland.

During this exploration you will have passed many fine parks as well as the Point Cabrillo Lighthouse. There is so much to see along this coast, it just might be worth more than one trip.

Thomas E. Cochrane is a California Professional Geologist who’s been prowling the landscape of Sonoma and Mendocino counties since 1976 and lives in The Sea Ranch. He’s the author of three books, including “Shaping the Sonoma-Mendocino Coast: Exploring the Coastal Geology of Northern California,” and a guest speaker for local clubs and organizations, including the Sonoma Land Trust. To learn more, visit RiverBeachPress.com