California’s Bonny Doon Beach is home to wide-open sands, a creek that runs through it, and even a clothing-optional section to the right of the chunk of Santa Cruz Mudstone where there used to be a natural bridge. It is also has a few features that tell of the areas railroad and oil exploration history.
Notice the Parking Lot
When you park to go to Bonny Doon Beach, the main parking area hugs right up to huge hill. It so happens this hill is a man-made embankment. The local stream used to run out to sea in the area where the embankment is now. If you have driven between Santa Cruz and Davenport, you might have wondered why you can’t see the ocean very often on the drive. It’s because every creek along the route has an earthen railroad berm or embankment across it that blocks the view. They were all built in the early 1900s, and the embankment at Bonny Doon Beach is a great example of a very big one.
Grandiose Railroad Plans
At the turn of the 20th century, railroads were king and still expanding with easy money from business tycoons of the day. The railroad embankments we see today were originally part of the Ocean Shore Electric Railway, which was begun in 1905 and was to be a grand line from Santa Cruz to San Francisco. It was to have two parallel electric lines to run both passengers and freight and be completed in 1907. Southern Pacific was also building rail to Davenport at about the same time, so there was definitely some hardball and power politics between the two companies.
A More Humble Reality
Fate intervened. The 1906 quake caused huge damages to the northern end of the Ocean Shore line, and their easy funding largely dried up. Construction continued, although money had to be raised from local bonds. Southern Pacific secured the contract to transport cement and materials for the Davenport Cement Plant, and that took away much- needed revenue from Ocean Shore.
The details of how the collaboration ultimately occurred are hard to pin down, but Ocean Shore and Southern Pacific collaborated in building the embankments north to Davenport. The embankments are so wide because they were designed for three tracks (two for Ocean Shore and one for Southern Pacific). They consist of wooden trestles filled in with local material to enable the structures to support the extreme weight of the railway cars loaded with cement.
By 1908, only portions of the rail on each end of the Ocean Shore line were running: Santa Cruz to Swanton, which is just north of Davenport, and San Francisco to Tunitas Creek, a few miles south of Half Moon Bay. The railroad never fully connected Santa Cruz to San Francisco. Ocean Shore stopped running trains by 1920 and never laid their second line. The Southern Pacific line was eventually sold to Union Pacific, which ran freight for the cement plant until the plant closed in 2010.
Why There Is a Tunnel
Creation of the railroad embankments meant completely blocking off the creeks and any associated estuaries and lagoons. Water flow was routed through tunnels made through the Santa Cruz Mudstone. The tunnels are on the north side of each beach and, despite large storms, have eroded little and have been adequate to handle the flow. In the picture below, the black arrow points to a tunnel where Liddell Creek comes out of the Santa Cruz Mudstone. You can follow the water to its exit at the ocean. The black rectangle shows the very linear railroad embankment that now defines the back of the beach.
There’s Oil in Them Thar Hills!
In the farthest-right cove at Bonny Doon Beach (yes, the clothing-optional section), a tall skinny dike of sandstone cuts across the Santa Cruz Mudstone. A dike is essentially loose material. In this case, it’s the older and deeper Santa Margarita Sandstone, which was squirted up under pressure through the younger but harder mudstone. The dikes and the Santa Margarita Sandstone contain bituminous (asphalt-like) material in varying quantities. There are many similar dikes in the sea cliffs along the north coast of Santa Cruz. This one is unusual in how skinny and rectangular it is.
Some of the bituminous sandstones just a few miles south, at Majors Creek, were quarried for paving material. Apparently, about 600,000 tons, valued at more than US $2 million, were quarried and sent by boat to pave San Francisco between 1888 and 1914. In the 1950s, the Husky Oil Company ran an experimental project to extract oil and gas by heating the sandstone in the drill hole and then recovering what melted. Over three years, they pulled out 3,000 barrels of oil and some gas. But costs were too high, overall, to make it economically viable.
Take the Self-Guided Mobile Tour
This piece is part of the North Coast Tour. Download the free app with many tours of the Santa Cruz area and beyond.
- North Coast Railroad Ramparts. Sandy Lydon’s Central Coast Secrets website.
- "The Geology from Santa Cruz to Point Año Nuevo—The San Gregorio Fault Zone and Pleistocene Marine Terraces," by Gerald Webber and Alan Allwardt, in Geology and Natural History of the San Francisco Bay Area: A Field-trip Guidebook: 2001. Fall Field Conference, National Association of Geology Teachers, Far Western Section, September 14-16, 2001. USGS Bulletin 2188, 2001:194.
- Living with the Changing California Coast, by Gary B. Griggs, Kiki Patsch, and Lauret E. Savoy. University of California Press, 2005.