^{Ring Mountain invites the eyes outward with superb views of the Bay, but looking down at its rocks is also a rewarding pleasure. All photos by Andrew Alden.}

California is known among geologists as a type locality for subduction. In everyday language this means a place that exposes textbook-quality examples of subduction-related rocks and tectonic features. The rarest and most scientifically precious of these is in Tiburon, and part of it is on pristine display at Ring Mountain Open Space Preserve.

I've shown you some subduction-related localities in previous posts: Deep seafloor in the Marin Headlands, pelagic limestone in Pacifica, and melange at Shell Beach on the Sonoma coast all represent the upper parts of subduction complexes. Ring Mountain lets us peek downward into their hellish depths.

The body of rock underlying the central Tiburon Peninsula is part of the large and sprawling Franciscan Complex, an assemblage of materials that was once involved in subduction. The oceanic plate whose small remnant is the Juan de Fuca plate, off Cascadia, has been subducting under North America for many millions of years. Most Franciscan rock is ordinary sandstone and shale, laid down offshore, that has been crushed and crunched in the subduction zone. Volcanic rocks on and in the oceanic crust are mixed in with these. The Ring Mountain block actually went deep down the subduction zone and somehow came back out. Thus it's a high-grade block, one that underwent a high degree of metamorphism. A large portion of it is serpentinite, yielding the typical toxic soil of a serpentine barren.

Amid that matrix is a large number of rocks bearing the signs of extremely deep burial recorded in their minerals. These have unfamiliar names like glaucophane, lawsonite, jadeite and actinolite. Together, they indicate very high pressure but relatively low temperature (specifically, pressures up to 2.5 GPa and temperatures of about 550°C). The ensemble is called blueschist, shown here.

The pressure corresponds to depths around 100 kilometers, but this is not a straightforward matter and the depths could be less than half that. The tale the minerals tell is one in which cold volcanic rocks of the seafloor were carried down quickly to these depths, not fully heating up. There the rocks were metamorphosed into a new set of high-pressure, low-temperature minerals. Then somehow the rocks returned with comparable speed to the surface, so that these minerals could not change back to their original species. (This retrograde metamorphism is why these minerals so rarely occur in surface rocks.) The rocks emerge totally changed.

The picture this conjures up is that of a packet of rocks being spat out of the subduction zone like a watermelon seed in the fingers. But geologists don't accept stories because they seem sensible; they use them as scenarios to test over and over against the rocks. That's where the conversation among the specialists sits today.

Ring Mountain is many other things to its visitors. Rock climbers like the bouldering and may not notice the streamlined shapes that resulted from the kneading action in the subduction zone.

Botanists love the flowers and plants endemic to the serpentine habitat.

Photographers love Ring Mountain because it offers everything from the large scale to the small, with an endless variety of light and subjects. If you go, take only pictures because every rock and plant is protected there.

Find out more about Ring Mountain's geology on "To See A World from Ring Mountain" by Jim Locke of the College of Marin.

37.909 -122.491

Tamalpais Manzanita, Mount Tamalpais State Park. Photo: randomtruth.

Serpentine, California’s state rock, is feeling some pressure—and not just because it’s a metamorphic rock! The California Legislature is considering a bill that would strip serpentine of its state rock status; geology blogger Brian Romans explained the details in this recent QUEST blog. Basically, proponents of the bill say that because asbestos is made from serpentine rock, and asbestos causes cancer, serpentine should not be the state rock. Never mind that serpentine does not cause cancer. In fact, many organisms thrive on serpentine soils. And that is what today’s post is about—the unique plants and animals that call serpentine soil home.

Serpentine soil is a tough environment: the soil is coarse, so water runs right through it, making it very dry. It is often dark in color, so it heats up in the sun. And its chemical makeup is challenging to plant life, to say the least. The soil has high concentrations of heavy metals, like nickel, iron, and chromium, and low concentrations of nutrients, like nitrogen and phosphorus. It is also really high in magnesium, which makes it hard for plants’ roots to take up those already-scarce nutrients. And it is low in calcium, which causes ion balance problems for plants.

With nutrients scarce, serpentine inhabitants tend to be small in stature—it’s hard to grow big without much food. And, with low water availability, serpentine plants are drought-tolerant. They often have tough little leaves, which don’t lose much water. Some examples are the Tamalpais manzanita (Arctostaphylos montana), and the Leather Oak (Quercus durata).

Plants on serpentine soils also have to deal with those heavy metals, which can interfere with metabolic processes. Some plants, like the Milkwort Jewelflower (Strepthanus polygaloides), have a really high tolerance for heavy metals. Milkwort Jelweflower is a nickel hyperaccumulator—it can take up lots of nickel from the soil, with no ill effects. In fact, some serpentine plants are used in bioremediation; people plant them in contaminated soil, where they pull the heavy metals out of the ground and sequester them in their tissues.

Serpentine soils are home to many endemic species—species that live in a particular habitat type, and nowhere else. Sometimes plants or animals are limited to one habitat because they can’t survive the physical conditions of other habitat types. But in the case of serpentine endemics, many can live in other habitats’ nutrient-rich soils, but are total weaklings when it comes to competition with other plants. They can’t live in other habitats simply because they are out-competed.

Serpentine soils are home to more than just plants—there are butterflies, too, like the beautiful California White (Pontia sisymbrii). Some, like a rare variant of the Edith’s checkerspot butterfly, Euphydryas editha luestherae, are serpentine endemics, because they lay their eggs exclusively on plants living on serpentine soils.

The Geoblogosphere is buzzing with commentary about California’s serpentine bill. If you feel passionate about keeping serpentine as the state rock, by all means write your state representative—but also visit some serpentine habitat! There are lots of places in the Bay Area where you can check out serpentine soils and their inhabitants. There are serpentine outcroppings on Mount Tamalpais, Mount Diablo (be sure to check out QUEST’s Mount Diablo State Park Exploration!), and in the Berkeley and Oakland hills.

37.879329 -122.2463347

Pacific Madrone

Marin will look Baja. Berkeley like Bakersfield.

That's the projection of climatologists for the end of this century, if global warming continues on its current path.

But in trying to determine what California's plant life will look like based on those projections, studies and computer models only go so far. Despite the dire warning raised by this recent plant-loss study, biologists say the reality probably will be a lot worse.

In trying to get your mind around the idea that two-thirds of California's endemic plant species will lose 80 percent of their range by the end of the century, there are two ways to look at it.

The first is that, well, plants will just be different. It's not as if we're going to have barren soil where plants are now. As climate changes and warms, plants will most likely shift to the north. If we're talking an 8.3 degree Celsius shift in the summers, that means a rise of about 15 degrees Fahrenheit during the summer. Desert plants would move into Bakersfield and the Central Valley, for example. And in the Bay Area, the climate would be more similar to Southern California.

So, one way to think about it is: Plants will migrate or shift to cooler climates, so our endemic plants wouldn't necessarily disappear – they would just shift north.

But there were many factors that were NOT included in the plant-loss projection. And, as study author David Ackerly says, they are sobering.

If plants migrate, where will they go, and how will they get there? They need a certain type of soil, a certain amount of water. Many times, they interact with and need the plants or animals around them to survive; for instance, the gooseberry might need an animal that likes its berries so that its seed can be spread. And they don't just get up and walk north. It's a long, laborious process that can easily be derailed.

During the last Ice Age, plants migrated a thousand miles, Ackerly says, over about a thousand years. So why can't plants here move a hundred miles in a hundred years? Let us count the ways.

So IF the soils are compatible, IF the entire ecosystem of plants and animals can successfully travel north, IF such sites as vernal pools can somehow be created in the north, IF those ecosystems can somehow leapfrog over cities, farms, reservoirs, roads, ranches and other developments and find a compatible area that doesn't already have a robust ecosystem, IF the slow-growing plants can somehow travel a mile a year for the next hundred years, then yes, you'll successfully have a new habitat in a different place farther north.

Biologists suspect that most endemic plant species in California will die, if climate change continues at the same pace. For instance, redwood trees could still be growing in California by the end of the century, because the adults are hardy – but scientists say it will be a forest of the "living dead," meaning that, if no seedlings can make it, those adults will be the last redwoods on earth.

And the plants that come in to replace California plants, they say, will be invasive species – more commonly known as weeds – the fast-growing Mediterranean-climate plants with light, airborne seeds that will take over a barren area.

That's different plant life, true. But it's unlikely, they say, that our madrone or bay ecosystems will actually be re-created a hundred miles away, unless we move them up there ourselves.


View a slideshow of the"Disappearing Plants" Radio Report online, as well as find additional links and resources.

37.404946 -122.244593