The Putah-Cache Bioregion Project:
Natural History and LandscapeWho | What | Where | Publications
Flora and Fauna
Historically all three watersheds drained into the Sacramento River in winter, so that forms its eastern boundary. The upper watersheds, in the Coast Range, are clearly divided from other watersheds by the mountain ridges. However, the watershed boundaries blur in the Central Valley. Relief is very low in the valley, so there are no clear divides. Also, the creeks and sloughs overflow during regular winter floods, and recharge the groundwater during summer. Thus the watershed area is not necessarily a question of what drains into the creeks, but what flows out of the creeks.
California weather is notably unstable, with regular periods of drought and flood; a "normal" series of years in the valley runs something like this: 12"; 25"; 18"; 22"; 15". In recent years (1994-1998) winter floods have occurred annually, but seven years of drought preceded them. The Coast Range gets about 40-60 in. of rain yearly, while Davis in the Central Valley averages about 17 in. per year.
The area near Clear Lake includes several currently inactive volcanoes, notably Mt. Konocti. Hot springs abound there, and a geothermal plant under Cobb Mountain makes use of the heat underlying the area.
The rest of the Coast Range portion of the bioregion consists of Franciscan melange (bands of muddy sandstone and chert, interleaved with basalt, and massively deformed), serpentine, and Great Valley Sequence seafloor (similar to Franciscan melange in age and composition but with much less deformation).
Associated with the volcanic areas and serpentine belts are mineral deposits such as mercury, sulphur, silver, and some gold.
The lower bioregion, in the Central Valley, rests on alluvial deposits that are literally miles thick. The Central Valley used to be an arm of the sea, but deposits from the Coast Range and Sierras gradually filled it in. The westernmost part of the lower bioregion, nearest the Coast Range, is somewhat rolling, but the area flattens until it is nearly plane at the Yolo Bypass. Because of the alluvium, gravel is mined around (and, until recently, in) Cache Creek.
Most drinking water comes from groundwater. Some irrigation water is also pumped from groundwater.
One lake in the bioregion, Clear Lake, is natural, the result of a landslide that dammed its original outlet. The other large lake in the bioregion, Lake Berryessa, is a reservoir created when Putah Creek was dammed in 1957. Virtually all other lakes in the region are also reservoirs.
Water quality and abundance are issues in the region. In the upper watershed, mercury leaches into the water. In the lower watershed, pesticide residues have been found in well water. The water itself is hard. Due to groundwater pumping, subsidence is a problem in some areas, particularly near Woodland. Creek fisheries have been affected in drought years because of water being diverted from the creeks.
In the Central Valley, virtually all land is urban or agricultural, and little remains of the original plant communities. Some riparian corridors survive, with oak, willow, walnut, and cottonwood trees. Tule and cattails are common in the sloughs. Native plants that once made up the valley prairie, such as California poppy, lupine, and owl clover, appear by roadsides.
The upper bioregion includes "charismatic mega-fauna" such as tule elk (originally valley fauna), black bears, mountain lions, coyotes, bobcats, and eagles, both bald and golden.
The lower bioregion is part of the Pacific Flyway. Thus there are abundant hawks and waterfowl during the fall and spring migrations. Many hawks and waterfowl winter here, and some live here year round. Egrets and blue herons are common. The rare Swainson's hawk nests here.
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