A few weeks ago my buddy Robert and I took an afternoon and went up to Bowling Ball Beach, a few miles south of Point Arena. Robert had never been to this beach before and he had really wanted to see it. This is such a fascinating place to hike around, and I took quite a few shots of this geological wonderland. I first posted about Bowling Ball Beach back in July of 2011. I thought it might be a good time to update that post with some new images and perspective.
The Bowling Balls
The main headliner at this beach is of course the ever-popular large bowling ball shaped concretions as seen in the first image, below.
This image is the classic view of BB beach, and yet there’s so much more to see there. But first let’s discuss the bowling balls themselves. These sandstone concretions were originally formed under great pressure deep on the ocean floor. Minerals of a similar content aggregate together around a common center and form, one micro-layer at a time, a denser and harder object than the softer sandstone around it. Most concretions are not anywhere near this large, which makes these Bowling Balls such a curiosity.
Moving up the beach one comes across several ‘muffin’-shaped concretions embedded in the uplifted strata of the bluff face, as shown in the following three images.
The first of these images shows the location of these flat concretions within the cliff face. Unlike the bowling balls, however, these concretions were formed from shale, cemented together by quartz at great depth. The second image shows the scale of these ‘muffins’ relative to Robert. Now, Robert’s from Texas where everything grows big, but even he had to admit to being impressed at these babies. These are huge by concretion standards. The next image shows us something else, namely how by viewing them obliquely one can see that these particular concretions were formed within the same plane, or strata. This image is a window into the specific layer of time in which these were formed. Many concretions are formed around fossils which alter the chemistry of the minerals around them, which may begin the concretion-forming process.
The bowling ball and ‘muffin’ concretions we see standing alone get exposed by weathering and wave action which erodes the softer material around them thus leaving them fully exposed. Eventually the ‘muffins’ we see in these images will be standing alone near where they lie today. The image below shows you just what I mean. In it, you can see the lone muffin half-planted in the sand at the base of the cliff, and if you look toward the top of the cliff, you can see another muffin still embedded in what was most likely the same layer as the one at the base of the cliff.
Layers of Time
So even though the bowling balls are the big draw here, this beach is really a study in stratification, the layering of various substrates over time…a lot of time. The next series of images not only demonstrate this stratification of the various layers of sandstone and shale, but also the extreme uplift that has occurred over the millennia.
The first image is a closer side view of some of the layering seen along this beach’s cliff face. Millions of years ago, these layers were flat (horizontal), and at considerable depth in the ocean. As the Pacific Plate slowly crept northward along the San Andreas Fault it also slid under the North American Plate, pushing the NA Plate upward and tilting it nearly vertical. The next image shows some of the unique formations of these layers across the cliff face. Looking closer in the last image, you can see the convolute laminations formed when these materials were created in the slowly swirling sediment. Weathering only accentuates these weird patterns in the sandstone. Standing in front of these formations also makes you also think you’re looking at a cobblestone brick pattern.
The next sequence of images shows the flatter, horizontal surface of the beach front.
This terrace is essentially a wave-cut platform. This flat intertidal area is formed by wave action which erodes and cuts away at the ridges in the sea floor. The first image shows what has been described by locals as “The Bowling Alley.” Subsequent images show other features of the broader marine terrace. The second image shows a little detail of some additional examples of the convolute laminations as seen in the face of the protruding ridge of the of the prominent ridge line. The stones and rocks lying in the alley were either left there after the surrounding material was washed away by erosion, and/or deposited there from the adjacent cliff face after being eroded away.
Erosion is a continuing process there, and you can actually hear it happening real-time if you stand anywhere near the cliff face. While we were there we could hear small rocks rolling down the cliff face and causing tiny landslides as they fell to the flat shelf below. If you look closely in the last image above you can see piles or fans of eroded sandstone debris at the base of the cliff face. Coastal zones are rarely static, and geologic processes are continually shaping and reshaping our beaches.
The next group of images merely shows some additional rocks and concretions which have found their way along the wave cut platform.
Can you find the ‘muffins’ in these images? Their shape and color are distinctive.
Of course any trip to the beach just wouldn’t be complete without some driftwood sightings, as seen in the next two images.
Driftwood is a great photo subject as it seems to capture the sense of the rawness of the beach, and its power to weather and transform natural objects into something, well…”beachy.” The first image just struck me as a unique piece of natural sculpture, while the intersecting lines of the redwood burl and rock strata in the second image just captured my eye.
The last image just brings us back full circle to the bowling balls which so aptly define this beach.
It’s hard to see all this in one visit, so I recommend several at low tide to see it all. Perhaps the first time you visit I recommend not bringing your camera so you won’t miss anything. This place needs to be observed and experienced fully before you start recording its many treasures. I hope you’ll make the trip, you’ll find it worth the effort.
For additional reading, you might consider Geologic Trips – Sea Ranch by Ted Konigsmark (1994) which also has a nice write-up on Bowling Ball Beach, and probably gives a better description of the geological processes than I tried to “cobble” together here.
Equipment: Nikon D3s, Nikkor 24-70 f2.8 lens and a monopod.