UC Davis ecologist Susan Harrison has returned with some photos about serpentine ecology. Susan’s captions are indented, and you can enlarge her photos by clicking on them:
Serpentine ecology at The Cedars (Sonoma County, California)
“Serpentine” might be a familiar word if you live in a region with volcanos, earthquakes, and hot springs. It’s an informal term for ultramafic (very high magnesium and iron) rocks, mainly serpentinite and its parent rock peridotite, as well as the soils formed from these rocks. The common name comes from the often snakeskin-like appearance of serpentinite. These rocks are twisted and fractured bits of the Earth’s mantle, first extruded into the ocean crust in midocean spreading centers, then fully or partly metamorphosed by hydration, and finally scraped onto land during the sliding of one tectonic plate under another – this last process being what also produces “ring of fire” volcanos and earthquake zones around the world.
Serpentinite:

Partly serpentinized peridotite:

Botanists and plant evolutionists have long been drawn to the unusual flora of serpentine. Most plant species are intolerant of its harsh chemistry, especially the scarcity of calcium relative to magnesium, and space is thereby opened for hardier species to adapt and sometimes even speciate on serpentine. In California’s flora of around 5,500 full species there are just over 1,000 “tolerators” that can grow either on or off of serpentine, and an estimated 255 “endemics” entirely restricted to this difficult soil.
Serpentine endemic plants in California include multiple Jewelflowers (genus Streptanthus, Brassicaceae), which have been studied to understand soil-driven adaptation and speciation.
Hoffman’s Bristly Jewelflower (Streptanthus glandulosus ssp. hoffmani):

Morrison’s Jewelflower (Streptanthus morrisoni), a non-flowering first-year individual:

Serpentine tolerators, like the Sickle-leaved Onion (Allium falcifolium), grow on varied soils. Sometimes they show adaptive genetic differences between populations on and off of serpentine.
Sickle-leaved Onions:

Today’s photos are from a May 2026 excursion to one of the most remarkable serpentine sites in the world: The Cedars in western Sonoma County, California. This site was named for its vast stands of Sargent’s Cypress (Cupressus sargentii), a serpentine-endemic tree.
The Cedars:


Part of The Cedars’ magic is that it’s a large (30 square km) and well-isolated block of serpentine within a benign coastal climate. This seems to be a winning formula for promoting plant evolution, as witness four full species and three subspecies found nowhere else in the world. Here are two species discovered by botanist Roger Raiche, who devoted decades to exploring and protecting The Cedars.
The Cedars Fairy Lantern (Calochortus raichei):

The Cedars Buckwheat (Eriogonum cedrorum):

A second charm of The Cedars is the surprising abundance of water in its austere landscape, probably because fractured serpentine rock masses tend to store rainwater and release it slowly, and also because many streams on serpentine have chemically cemented beds that create deep pools. Streambanks here are fringed by Western Azalea (Rhododendron occidentale), Serpentine Columbine (Aquilegia eximia), and the two showy orchids shown below.
California Lady’s Slipper (Cypripedium californicum):

Giant Stream Orchid (Epipactis gigantea var. rubriflorum; photo by Nishanta Rajakaruna): \

The piece de resistance, sine qua non, ne plus ultra of The Cedars is its mineral springs. Until geologists discovered the strange chemistry of these springs in the 1960s, it was not known that serpentinization, the hydration of mantle rock, could occur in near-surface terrestrial environments. Serpentinization supports anaerobic microbes that are collectively the most abundant life form on Earth; they are considered strong candidates for the origin of life, as well as for the possibility of life on other planets.
The spring known as Mineral Falls:

Part of the spring known as Wedding Cake:

Animal life is relatively scarce on serpentine. Here are two of only 8 bird species we saw in a full day at The Cedars.
Violet-Green Swallow (Tachycineta thalassina) hunting above Austin Creek:

Peregrine Falcon (Falco peregrinus) perched in the middle of a towering cliff:

JAC: I told Susan I couldn’t see the falcon, so she sent me a photo with the bird circled:

My friend Nishanta Rajakaruna has devoted his career to studying serpentine ecosystems around the world. On field trips like this one, he collects photos of people leaping.
Leaping on serpentine (photo by Nishanta Rajakaruna; that’s me on the right):
