Most California residents know that the state flower is the California poppy and state animal is the grizzly bear—but do you know the state rock?
It’s serpentine, a greenish, waxy rock that occurs where oceans once collided with continental plates and were exposed above the Earth’s mantle due to tectonic activity. Over time, the rock eroded into rare soil, which now represents only about 1% of California’s land—much of it right here in Santa Clara Valley. Over recent years the majority of our serpentine soil has been covered by human development such as houses, roads, and businesses. The single largest, untouched block of it (measuring 15 x 2 miles) can still be found in Coyote Valley, just east of Highway 101.
A Harsh Habitat Where Native Plants Thrive
Serpentine soil is notably low in calcium and nitrogen, and high in magnesium and heavy metals such as nickel and chromium. This unique mixture creates a harsh and even toxic environment for many plants. Several native species have adapted to this soil and thrive in it, making serpentine areas perfect spots for viewing indigenous plants, trees, and flowers.
Today, many of these plants are at risk; their habitat is shrinking due to ongoing development. The California Native Plant Society has identified 15 plants in the Coyote Valley region alone as rare or endangered, and five of those are on the federal endangered list: the Santa Clara Valley dudleya, the coyote ceanothus, the Tiburon Indian paintbrush, the Mt. Hamilton thistle, and the Metcalf Canyon jewelflower. While It’s only the loss of habitat that threatens these species, vehicle exhaust affects them as well.
Vehicle exhaust—which is very high in nitrogen—actually acts as a fertilizer for some competing non-native species. The more exhaust from nearby Highway 101, the more non-native plants grow and crowd out native plants that have adapted to the low-nitrogen soil. Land stewards have found that controlled cattle grazing helps alleviate the problem, as the cows prefer to eat invasive, non-native plants, clearing space once again for native species to flourish.
The rarity of plants in our local serpentine areas also impacts the threatened Bay Checkerspot butterfly. As a caterpillar, it feeds solely on dwarf plantain and purple owl’s clover wildflowers that grow in serpentine areas. The Coyote Valley area contains the last remaining healthy population of these butterflies, which are considered a threatened species by the US Fish & Wildlife Service.
Enjoy This Rare World
We invite you to come explore the serpentine habitat right here in your own backyard via hikes, bike rides, guided walks, and other activities in Coyote Valley. Not only will you see thriving native wildflowers, but you may even spot a butterfly that lives nowhere else in this world! And it’s all due to our unique soil. Check out upcoming events or ways to get involved in Coyote Valley to see for yourself.