Santa Cruz’s Natural Bridges State Beach
October 06, 2017
The very name of Natural Bridges State Beach, in Santa Cruz, California, is a clue that geology happens — sometimes surprisingly quickly. Despite the plural use of bridges, only one arch is visible at this site today. In the photograph here, taken on June 24, 2017, that lone arch reaches out into the Pacific Ocean, beyond children playing in the surf. Note that as other wading beach-goers try to find a perch on the stony stack’s edges a flock of California brown pelicans also happens to be flying by.
In the course of a long human lifetime — between 1906 and 1980 — the natural arcs that gave this location its name went from three windows, in a single peninsular finger of marine Santa Cruz Mudstone, to just one. A historic photo in the Special Collections at the University of California at Santa Cruz shows the formation in about 1900. It is presented together with other photos on a Mobile Ranger Web page, accessible here.
Santa Cruz Mudstone consists of fine-grained silts, clays and single-celled plankton called diatoms, which settled on an offshore continental shelf or slope during the late Miocene, 7-9 million years ago. The thick, yellowish-brown siliceous and organic layers cemented and lithified into rock, and have been subsequently folded and faulted and tilted and twisted by tectonic stresses. The mudstone resists the pounding oceanic waves, but time and erosion took the outermost of the triplet bridges in 1905 or 1906, leaving just a temporary stump, historians say. Then, during a storm on January 10, 1980, the innermost bridge also collapsed, leaving today’s lone opening. And someday, as Alexander Weiss observed in his “Ode to an Arch,” penned soon after that 1980 tumble, the remaining window, too, will vanish:
For through erosion it was born
And through erosion it would die
And such a death one does not mourn
One merely says goodbye.
Photo Details: Camera Model: NIKON D3200; Lens: Tokina AT-X 124 AF PRO DX II (AF 12-24mm f/4); Focal Length: 15mm (35mm equivalent: 22mm); Aperture: ƒ/11.0; Exposure Time: 0.0020 s (1/500); ISO equiv: 280.