Where the Sierra Nevada Rises From the Sea: Birds and a Hole in the Head at Bodega

Sea stacks at Bodega Head, with the Point Reyes peninsula in the distance

We are reaching the end of my series on the Central California coastline from Big Sur to Bodega Bay. I've been calling the series "Where the Sierra Nevada Rises From the Sea" for a very specific reason. Much of this section of the coast is composed of granitic rocks that formed in the subduction zone complex that was the origin of the Sierra Nevada batholith, the 400 mile long block of granite that is the backbone of California. The rocks, known as the Salinian Block (or Terrane), have been displaced hundreds of miles northwest by lateral motions along the San Andreas and related fault systems over the last 30 million years or so. Bodega Head is the northernmost exposure of these granitic rocks.

Bodega Head refers to the former island of granitic rock that is now connected to the mainland by a large area of active and stabilized sand dunes. Bodega Bay formed between the head and the mainland, and is nearly closed off on the south side by a sand spit along Doran Beach. A small marina is here and a modest fishing fleet works out of the harbor.

No, this isn't a bird attack at Bodega, but I sure thought about it while I was snapping this shot of Red-wing Blackbirds at San Luis National Wildlife Refuge near Los Banos in the Central Valley.

One may not know Bodega for the geology, but there are those who will remember Bodega Bay as the setting for a rather famous movie about our avian friends, The Birds, Alfred Hitchcock's classic. The original house where many scenes were shot is gone now, but the cypress grove where the house stood can be seen on the sand bar that connects the Head to the mainland. The land is owned today by the University of California, which runs a research facility at the site (occasional tours are offered).

Bodega Head has a horror story that may be the equal of an unexplained attack by our feathered companions. The rock sequence found east of the San Andreas fault is part of the Franciscan Complex, and these rocks are notorious for their slope-failure tendencies. Mass wasting is a way of life for anyone who chooses to build on it. Bodega Head on the other hand is composed of hard granitic rock. No slope failures would be expected there.

The Hole in the Head

So it was that in the 1950s that PG&E looked with great longing at the granite headland and decided that Bodega Head would be an ideal spot for a brand new nuclear power plant. The water they needed was there, there was solid ground to build on in contrast with the lousy slopes east of the fault in the Franciscan Complex. And not that they thought of things this way back then, but the site was fairly isolated from large population centers in case of bad accidents (which we all know NEVER happen with nuclear power plants).

And adjacent to the San Andreas fault! Its not like they didn't know it was there. In 1906, this part of the San Andreas shifted 15 feet or more. So they began digging a hole that would serve as the foundation for the power plant. As the plans and excavations progressed, local opposition began to grow, and ultimately the company somehow realized they were about to put a nuclear reactor practically on top of the San Andreas fault (subsidiary faults were discovered in the excavation pit; a geologist opined that “a worse foundation condition would be tough to envision.”). The pit became known as the "Hole in the Head".

So the nuclear power plant was never built, and Bodega Head remains as barren windswept ridge with beautiful cliffs composed of the northernmost exposures of the granitic rock of the Sierra Nevada. The Hole in the Head filled with seeping groundwater that now supports the local wildlife.

And so ends our little series of a part of the Sierra Nevada mountains that rise from the sea. I hope those of you who've followed it enjoyed the journey. I'll be putting up a compilation of the different posts in the series since it has been a rather off and on project over the last three months!

Seeking Geology Along the Most Beautiful Shoreline in the World: the Central California Coast

Oh, I know that the title of this post is a bit of hyperbole...there are many beautiful coastlines in the world, and you are free to argue for your favorite in the comments. But I think that geology has dealt a special hand to the part of California between San Simeon and Bodega Bay on the California Coast. It's hard to think of a more diverse place of intriguing scenery, with fascinating geological relationships at the same time.

I had two occasions in recent months to explore this most beautiful region; a three day trip with my students, and a spur-of-the-moment camping trip. We didn't visit every beach along the Central Coast, but we found several spectacular state parks, and I was reminded at every turn of the road what an incredible place live in. California is a wonderful place...

Here's a bit of a preview...we'll have a look at Julia Pfeiffer Burns State Park and wonderful McWay Fall, which at times falls directly into the sea.

We'll explore little-known Garrapata State Park, a stretch of beach that is pleasingly deserted much of the time.

Point Lobos State Preserve is better-known, but it also has a wonderful geological story: just where did those incredible conglomerates come from?

 Point Lobos also has some intriguing sea arches.

And Bodega Head...what is the Hole in the Head, and what stupid thing was nearly done here in the 1950s? I hope you will enjoy the journey!

The Other California: I Need This Like a Hole in the Head

What happens when profit motive collides with good science? I dunno, I'm on vacation!

We escaped the heat of the Central Valley yesterday by taking a drive up Highway 1 from Bodega Bay to Fort Bragg. Bodega Bay is formed by a prominence called Bodega Head that would otherwise be an island, except that sand has linked the island to the mainland and in the process formed a small protected harbor. The Head is a beautiful stretch of coast, with some stunning seacliffs and sea stacks on the Pacifc side.

Many of the seacliffs in this part of the state are formed out of Franciscan sediments or Neogene sandstones, so the cliffs at Bodega Head stand out. They seem steeper and more resistant. A quick look at some boulders at the top of the cliff soon make it clear why:

The rocks are made out of granite! Or, to the geologists eye, a granitic gneiss (note the lineations in the boulder above). These rocks have undergone some stress. The granite seems a bit out of place considering the big California picture; we tend to associate granite with the Sierra Nevada or Southern California, not the North Coast.

Which brings me to this scene, from the bay side of the Bodega Head. There is a quiet little freshwater pond, surrounded by thick vegetation. There was a gathering of egrets in the trees, and despite the season, wildflowers were in abundance. It was a serene setting.

What wasn't clear from the ground perspective is the pond is rectangular. It's artificial, having been dug out of the solid granite, but it was abandoned for some reason and left to be reclaimed by nature. Groundwater maintains the water level. So what happened here?

It turns out that in the late 1950's, an electric utility wanted to build a nuclear power plant on the site. The granitic rock would provide a firm foundation, there was a plentiful supply of water for use as a coolant, and the site was close enough to the Bay Area that transmission infrastructure costs could be kept low. What could go wrong? So they dug this hole to prepare the foundations for the nuke plant.

What could go wrong? We need to ask again what granitic rock is doing here. It is indeed out of place, for this rock originated to the south. At least 200 miles south! It was split off and carried north, 10-20 feet at a time during major earthquakes. There have been perhaps 100,000 of these earthquakes in the last 15-20 million years. As we look across Bodega Bay in this last photograph, we come to realize that Bodega Head lies on the Pacific Plate, while the town of Bodega Bay lies nestled on the North American Plate. The San Andreas fault passes within a few hundred yards of the chosen site for a nuclear power plant!

It is said that local opposition led to the abandonment of the project. Maybe. I've heard that they found evidence of active breaks in the granite within the pit. In any case, it never got built, and today the locals refer to the pond as the "Hole in the Head".

The Other California is a series of blog posts highlighting the kinds of places and features you don't find on the postcards of our beautiful state.