A section of trench at the southern end of the project without the steel-wire and rope-net barrier fence.
Along Highway 1, sandwiched between the elephant seals at Año Nuevo State Park and the colorful kite surfers at Waddell Beach, is a 1.4-mile stretch of coastline called the Waddell Bluffs. These near vertical bluffs, made of Santa Cruz Mudstone, are so steep and prone to erosion that they simply defied safe and reliable traversing for almost a century.
The bluffs and adjacent creek and valley are named after William Waddell who conducted timber operations there in the 1860s. At that time, stagecoaches could only pass the bluffs by waiting for low tide and using the hard packed sands of the beach. During winter, passage by beach crossing or even in a boat was essentially impossible and residents couldn’t reasonably reach the county seat in southerly Santa Cruz. In a surprising nod to geography over politics, Santa Cruz County allowed the area north of the bluffs to be annexed to its northerly neighbor, San Mateo County, in 1868.
An Engineering Nightmare
Even with the development of heavy machinery, engineers struggled for several more decades with how to construct safe passage over or past the cliffs at a reasonable cost. The Ocean Shore Electric Railway couldn’t complete a continuous railroad between San Francisco and Santa Cruz during 1905 to 1908 because of the Waddell Bluffs. The State of California acquired the land in 1933 but didn’t come up with a viable roadway design until 1941. The project was delayed due to WWII, but did begin in 1947 and was completed in 1948.
The design essentially cut into the slope and then used the material as fill to create an adjacent, flat roadbed along the beach. A massive 600 foot long retaining wall was built to protect the section exposed to the worst wave erosion. The retaining wall consisted of huge boulders weighing up to 11 tons each (called rip-rap). The original rip-rap was quarried granite from 8 miles away. The excavation of the bluffs alone moved 1.1 million cubic yards of material (52 football fields filled to a depth of 10 feet).
Erosion Never Stops
A debris trench 15 feet wide, 4 feet high, with a 2 foot berm separating it from the highway, was also constructed to catch falling pieces of rock. This design took advantage of a fortuitous property of the Santa Cruz Mudstone; it rarely falls as large blocks. Instead, it tends to break apart in small chunks. This produces a relatively manageable rain of debris, which can be removed periodically from the trench.
Unfortunately, large blocks do occasionally come down and bounce onto highway one. In the 1990s, a man traveling north in a passenger truck was killed by a rock that bounced through his front window. Litigation after the accident accused Caltrans of improper maintenance and emptying of the debris trench. Thus in 1994, Caltrans installed the steel-wire and rope-net barrier fence that is there today.
To maintain the depth of the trench, Caltrans annually removes 15 to 30,000 cubic yards of rock (0.7 to 1.4 football fields filled to 10 feet) and places it onto the beach. Winter storms entrain it into the ocean currents and carry it southward. Without the highway the rock would have fallen onto the beach and moved into the ocean currents naturally. Studies mandated by the California Coastal Commission have not found any adverse ecological impacts from this method of rock removal.
Erosions Many Forms
Not only are the rocks falling from the Waddell Bluffs a constant hazard, the roadbed is essentially on an active beach and is attacked by waves. The El Niño storms of 1983 removed all of the loose rock and fill protecting the highway at their southern half. This section was repaired and reinforced with rip-rap within that year.
Whenever I drive on those bluffs, I can’t help but imagine falling rocks or a huge slide. I always wonder how that weird fence will react and if that circled wire will really provide the needed flexibility to hold in the kinetic energy. I think my foot gets a little heavy in an effort to get me out of there fast.
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- Calculations for Volume Analogies. Math Central Website. http://mathcentral.uregina.ca/QQ/database/QQ.09.13/h/john1.html
- 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: Stoffer PW, Gordon LC, eds. 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. USGS Bulletin 2188; 2001:194.
- Living With the Changing California Coast. Gary B. Griggs, Kiki Patsch, Lauret E. Savoy. University of California Press; 2005.
- Rancho Del Oso Nature and History Center Website. http://ranchodeloso.org/history/
- Wadell Bluffs, Illustrated. California Highways and Public Works. Official Journal of the Division of Highways, Department of Public Works, State of California. Kenneth C. Adams Editor. September-October 1948. Volume 27, Number 9, 10.