Serpentine soil
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September 16, 2023
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Serpentine soil is all over Marin County. This soil type can be found on Mt. Burdell, Bowman Canyon Preserve, Ring Mountain, Old St. Hilary’s Preserve, and Mt. Tamalpais. What’s so different about it? The gray green appearance of the parent rock is distinctive. Its chemical makeup is high magnesium and heavy metals, and low calcium and nitrogen. This combination makes it a difficult growing medium for plants.
At Ring Mountain some rare plants grow: Tiburon mariposa lily, Calochortus tiburonensis; Tiburon jewelflower, Streptanthus glandlulosus niger; Indian clover, Trifolium amoenum. The agency One Tam started a Serpentine Endemic Occupancy Project in 2016. The rare plants recorded on Mt. Tamalpais include buckwheat, Eriogonum luteolum caninum; serpentine reed grass, Calamagrostis ophitidis; and Mt. Tam manzanita, Arctostaphylos montana ssp. montana. All of these are ranked 1B, rare and endangered, with the exception of the reed grass that is ranked 4.3, limited distribution.
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Katie Martin