Natural History
Geology -- The Preserve is in a huge volcanic field, the “Sonoma Volcanic Formation.” Geologists judge it to be between 3 and 7 million years old - rather young in geologic time! The Sonoma volcanics cover much of western Napa County, including mountains on both sides of Napa Valley, the eastern quarter of Sonoma County, and the southwest quarter of Lake County – an area of about 350 square miles. Huge amounts of lava and ash were deposited over this area. Geologists have not found volcanoes in the area and hypothesize instead that scattered fractures in the Earth’s crust may have been the source.
Volcanic deposits on and near the Preserve are mainly lava and ash. Ash forms into soft white layers called “tuff.” Curious structures called “columnar lava” or “volcanic postpiles” occur on the Preserve, visible at the swimming hole near the bridge and high up the creek. Like those of Devil’s Postpile east of Yosemite, they consist of large columns of rock tightly joined together. In the creek bed of the Preserve, some large columnar fragments can be found, showing these 5- or 6-sided posts clearly.
Plants -- The redwood trees were logged in the 1890s. In several dozen places, sawed-off stumps can be seen, often ringed with new trees sprouting from the roots or bases of the stumps. Due to logging, this forest is not old-growth redwood, but some very old trees can be seen. The other tall conifer found here is Douglas-fir, identified by its dark, thickly furrowed bark and long blunt single needles.
Fires occurred on the Preserve in 1906, 1945 and 1996. All three burned from the Sonoma side over the ridge to Napa County, varying in their extent and damage. Fires that burn through the undergrowth protect the land from more damaging crown fires. Some of the redwood trees show black scars on their bases resulting from these fires. The bark of the redwood protects the tree from the heat and damage of fire.
Ferns abound in the redwoods. Sword Fern is evergreen and often grows in large clumps. California Polypody, Polypodium californicum is a small winter-growing species with tender lance-shaped leaves or “fronds.” Bracken fern, a summer plant, has fronds far larger than Polypody’s.
Many other interesting native plants grow here, including wild strawberries and huckleberries. The latter plant is closely related to the domestic blueberry. Huckleberries on the Preserve bear fruit when they receive enough sunlight, but most live in the creek where it is too dark. Above the creek and higher up live the manzanita and madrone trees.
Several species of oak appear on the Preserve. The California Black Oak has large, deeply cleft leaves with bristle-tipped lobes. Shrub Oak is a shrub rather than a tree.
California bay trees are prolific in the Douglas-fir and oak woods. Unlike oaks, California bay trees are known for their long and strongly-scented lance-shaped leaves. These leaves may be used in cooking as a substitute for laurel leaves.
There are a variety of wildflowers that bloom on the Preserve, including Western Heart’s Ease or Two-Eyed Violet, whose white flowers have yellow bases and two purple “eye-spots,” and Trillium, a plant with three leaves per stem and white or pink three-part upright flowers.
Wildlife -- Animals on the Preserve include deer, fox, mountain lion, raccoon, skunk, gray squirrel, and an occasional bear. Red-tailed hawks and buzzards are often visible. Other bird species abound in the forest, including the large pileated woodpecker, with a red top-knot and piercing call, “kee-kee-kee-kee.” Sometimes they can be heard “drumming” loudly on tree trunks. Spotted owls, larger barn owls, and tine pygmy owls are also found here. Although rarely seen, they can often be heard calling in the forest.
Snakes, lizards, frogs and salamanders are also present, including the western newt, a kind of salamander with a dark orange belly that likes moist places. Trout can be seen in the larger pools, and minnows are almost everywhere in the creek. Steelhead trout do not come onto the Preserve, but they were often seen in great numbers downstream where the creek can be seen next to the county road.
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