Tuesday, January 27, 2015

Dana Point geology trip

On Saturday, we took a trip to Dana Point. A friend of ours we hadn't seen for over five years - but we have kept in touch with via mailing lists and Facebook - teaches a class on Earth Science, and local beach Dana Point is one of the field trips, where he gave a detailed presentation.

The 'point' in DP is a lump (technical term) of San Onofre Breccia, which is harder than the younger Capistrano Formation beside it, and comes to prominence at the point.

According to Caltrans,

The Early-Middle Miocene San Onofre Breccia: [...] great landslides fell down the slopes of a large landmass west of our present coastline. Catalina Island is a remnant of that landmass and cyrstalline Catalina-type rocks were eroded to form the San Onofre Breccia. The breccia formation has been uplifted by faulting and forms the headland of Dana Point. An estimate is that the speed of the landslides must have at times exceeded 100 mph to create such a large boulder breccia. The rocks and minerals include asbestos, serpentine, actinolite, fuchsite, epidote, chlorite, glaucophane, pyrite, magnetite and quartzite.

The Late Miocene to Early Pliocene Capistrano Formation: The marine Capistrano Formation is found in the southern part of the county. It ranges from Late Miocene to Early Pliocene in age and consists of poorly consolidated, fossiliferous, sandy-siltstone and mudstone. Sediment failures have caused extensive landsliding in the San Juan Capistrano and San Clemente areas. Turbidite deposits may be seen in the sea cliffs between Dana Point and San Onofre. Turbidites are deposits of marine sediment formed by undersea mud slides or turbidity currents that dump sediment into graded layers: the larger-sized gravel falls first, followed upward by progressively finder sediment grains. the base of the turbidite is a sharp accumulation of the coarse gravels. The top of a turbidite deposite is often difficult to define because the fine-grained, last to settle sediments, blend with the natural "grain size" of marine sediments. 


Our friend Professor Phil giving a presentation about the 
cliff of San Onofre Breccia. (My photo.)

A short walk off to the right of that picture is the junction of the San Onofre Breccia with the Capistrano Formation, and therein lies a tale. 

Dana Point is quite lovely, and the locals have always had a fascination with building as close as possible to the edge of the cliffs so the inhabitants can admire the view. More or less concurrently, they've always moved to edge out surfers - who used to love Stillwater Bay and its long pier - in favor of hordes of yacht captains who pay massive berthing fees just to have a boat in the water. 

So Dana Point used to look like this: 

That picture is from this site, which has great pictures and anecdotes about DP's surfing history. 

In the twenties, Sidney Woodruff, developer of Hollywood(land), wanted to build Dana Point Inn on the top of the cliffs just to the right of the picture above. He built concrete arches and some of the superstructure directly on the edge of the cliff, and put in a tunnel (through the soft Capistrano Formation) to the bottom of the cliff as an elevator shaft. 

The Depression interfered with his plans, and all that's left of the Inn are the concrete arches, still perched at the edge of the cliff.  (Photo above from this page.)

The tunnel ended up being used for bootleg liquor shipped in from Mexico and smuggled to a speakeasy above. 

Here's Phil talking to his students about Prohibition. (My photo.) You can see how far back the cliffs have retreated by the way the tunnel door is no longer flush with the rock. 

This is what the Capistrano Formation looks like, just to the right of the picture above:
 (My photo.)

And here's a piece of rock from the cliff the builders have left on the ground, presumably so Geology Professors can explain the history of the rock.

(My photo.)

So the 1920s adventure came to naught. However, from the forties on, people were determined to monetarize Dana Cove. In the early 1960s, Dana Point was being prepped for the new harbor, and now looked like this:
(Photo is a crop of a postcard.)

You can see the dirt track is now a road sloping up from center to top left, with grading below, and some shoring up has been done on the fault where the red San Onofre Breccia to the left meets the sand-colored Capistrano Formation, top  right.

In 1971, Dana Point Harbor was built, with space for 2,500 yachts. The pier was shortened, a breakwater was constructed (to the dismay of the surfers) and a great deal of concrete was strewn about to keep the sea away from the cliffs and generally build things. At that time a restaurant was proposed, called The Quiet Cannon, to sit exactly on top of the fault right at the edge of the cliff. According to this paper by Scott Kerwin, it was generally known to be a not-unarguably-good idea even at the time, but the restaurant went ahead. When the inevitable slope failure occurred in 1980 the restaurant (now called Cannons and a really nice place to get Sunday Brunch btw) sued Orange County.  The County accepted responsibility for clean up, and shored the cliff up. There's a detailed explanation in the above paper, and two illustrations, which I've cleaned up a bit to post here. 


The landslip under Cannons. (Photo from Kerwin.)



Remediation: A crib wall at the bottom, and a concrete structure at the top of the cliff, held in place by greater than 100 foot long rock anchors. (Photo from Kerwin.)



^^ If I'm reading that report correctly, San Juan Capistrano is basically made out of pudding with pebbles in it, on a steep tilt, and the land is likely to disappear under me at any moment. 

In the 21st century, Dana Point looks like this:


Although this looks south-east, opposite direction to photos above, you can orient by the the pier, visible nearly half way up and just to the right left of center. 

According to habig.com, there is a time capsule beneath the rock work of the harbor due to be opened on August 29th, 2016, 50 years after the surfing at Killer Dana came to an end. Exciting!

Oh, and it was nice talking to Phil as well. :)

2 comments:

Carroll McNeill said...

Geology!
History!!
Friendship!!!

I tell ya, this post has it all!!!!

Lyle Hopwood said...

And splashing inadvertently in the Pacific when a big wave comes in unexpectedly.

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