The Santa Cruz Sandhills: Windows into the Miocene
In between Bonny Doon and Scotts Valley, small windows into the Miocene Epoch pock the Santa Cruz Mountains. At first glance, they might be easy to dismiss — barren stretches of sand occupied by hardy, arid chaparral scrub or pine. Yet look a little closer, perhaps as you hike the Sunset Trail above Quail Hollow Ranch or along the edge of Henry Cowell Redwoods State Park.
In soil white and fine as beach sand, tiny, unusual flowers bloom. Bizarre, one-of-a-kind insects crawl among rare lizards. Beneath the surface lurk ancient mollusks, urchins, the fossils of uncanny marine creatures and long-extinct algae and plants. To dig into the story of the Santa Cruz Sandhills is to tumble back, back, back…10 million years.
In the Miocene, the Santa Cruz Mountains aren’t mountains at all.
They are the bottom of a vast, yet shallow ocean — no more than 325 feet at its deepest — that stretches east into what is now the Central Valley. All kinds of remarkable organisms hunt and graze in this ancient ocean — gigantic carnivorous sperm whales and 50-ton sharks, early forms of dolphins and pinnipeds, and 2,000-pound sea cows.
As plants and animals live and die over the millennia, their remains drift to the seabed below, creating a vast deposit overlain with sediment. This monumental accumulation eventually hardens into a mix of sandstone and siltstone. As the Miocene progresses, a cooling period arrives and the oceans recede. Over time, parts of the soft stone are weathered down to a porous, high-grade sandy soil. Then, roughly a million years ago, great blocks of the earth’s crust are thrust upward. Faults fracture the surface. Some of these blocks tumble downward. The Santa Cruz Mountains are born. As these enormous segments of Earth accordion and fold in on one another, they expose slivers of that ancient Miocene ocean floor.
Today, those sandy pockets are both a rich fossil record of the Miocene Epoch and one of the most delicate and unique habitats in the world — the Santa Cruz Sandhills.
Only 3,960 highly fragmented acres remain, yet they support four plant species and two insect species found nowhere else in the world — plus isolated populations of two lizard species, and the last known population of the Santa Cruz kangaroo rat. Biologists believe they will discover at least eight to ten new species unique to the sandhills ecosystem with more research. The sandhills are also home to ponderosa pine and succulent flowering pussy paws, two species typically found only in the High Sierra.
Unfortunately, before we understood how diverse and fragile it was, we allowed residential development, agriculture, and sand mining to alter or destroy more than half of the Santa Cruz Sandhills back in the 20th century. As these sand mining operations extracted tons of the highly pure sand for use in structures and silicon chips, their quarries occasionally coughed up some remarkable visitor from the geologic past. In 1963, for instance, the Olympia Quarry divulged the intact fossil of a 10- to 12-million-year old sea cow.
Of course, without a strategy to protect and rejuvenate them, the Santa Cruz Sandhills and their fragile ecology may go the way of the Miocene sea cow.
Fortunately, there’s a plan. In her 2004 conservation and management report, biologist Dr. Jodi McGraw lays out a blueprint for habitat preservation:
1) Prohibit further human disturbance. Only one sand quarry remains active in the mountains, but recreation accounts for continued habitat degradation. When visiting the sandhills, always remain on the trail. The burrows of the Santa Cruz kangaroo rat, a small rodent found only in the Santa Cruz Sandhills, are particularly vulnerable to off-trail shenanigans.
2) Control invasive species. Brooms, acacia, and eucalyptus are diabolical. They grow fast, spread faster, and are really, really difficult to kill. To complicate matters, broom growing in the Sandhills cannot be pulled by hand as it disrupts the endangered Mount Hermon June Beetle, another endemic species.
3) Conduct controlled burns in the sandhills. After a half-century of fire suppression, shrubs and trees have encroached on the sandhills, diminishing their total habitat area and building up fuel for a potentially catastrophic fire.
Education, interpretation, and outreach programs to increase public awareness and appreciation for the Santas Cruz Sandhills are also crucial to long-term preservation. “When people are aware of the uniqueness, rarity, and fragility of the sandhills, they are more likely to comply with regulations, support local conservation efforts, and actively work to protect habitat,” said McGraw.