Rocks With Spots!

Natural Bridges State Beach, located at the western edge of Santa Cruz, California, is a great place to play in the sand, explore tide pools, and marvel at the single remaining "natural bridge".  Early photographs show that there were originally three dramatic arches here.  However, by the mid-1970's, two arches had collapsed, leaving just the one (for more information on this, see Santa Cruz Coast: Then and Now, Arcadia Press, 2006, pages 27 - 28)

As you climb up over the rocks to get a closer look at the tide pools, you stumble upon something else that grabs your attention: unmistakable markings on the rocks underfoot that look like spots of varying sizes, forming spiraling patterns and lines.

These warm brown, slightly faded spots and lines dance around the sun-kissed surfaces in counterpoint to the inherent jointing in the rock.  They create bold, yet harmonious compositions everywhere.

Coastal geologist and oceanographer, Gary Griggs, says that this rock is Santa Cruz mudstone, and the markings were most likely created by the process of iron oxide precipitation.  Apparently, a rock's exposure to a variety of biological processes, in addition to salt water spray, runoff and seeping ground water, can markedly alter the way rocks look.  In his book, Introduction to California's Beaches and Coast, he writes:

"The fractures or joint patterns are usually due to the stress the rocks have been exposed to in the eons since they were formed, and these fractures tend to occur in geometric patterns.  As the water seeps into the cracks, the iron contained in the water will gradually precipitate out, leaving rusty iron oxide marks behind as the water slowly dries out or evaporates.  The stains will form in different geometric patterns based on the rock structure and weaknesses that water has been able to penetrate. The leopard spotting results from the same iron oxide precipitation process but may be a result of microbial activity within the rocks that was spaced out somewhat uniformly within the cracks in the rocks and served as points where the iron could be precipitated more easily."

Photo courtesy of Gary Griggs

Photo courtesy of Gary Griggs

How fascinating that a natural process can create distinct markings, as if guided by a sentient hand. Just looking at these images makes me want to head out to Natural Bridges State Beach very soon to see what other mesmerizing compositions I can capture...so stay tuned...

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