Suburban Vernal Pools EarthCache
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Vernal pools are seasonally flooded depressions found on ancient soils with an impermeable layer such as a hardpan, claypan, or volcanic basalt. The impermeable layer allows the pools to retain water much longer then the surrounding uplands; nonetheless, the pools are shallow enough to dry up each season.
After the hardpans formed, changes in the climate and vegetation resulted in different weathering and soil forming processes. Clays generally form in a more humid climate; hardpans form in a semi-arid climate, the same kind of climate that exists in the Sacramento Valley today. Certain types of clays form in certain types of soil weathering processes. The clay can also move downward in the soil profile by the percolation of rainwater where the clay was deposited on top of the hardpan. The clay is a type of clay that swells when it is wet, making it even more difficult for any more water to pass through. The claypan also contributes to the soil impermeability making it possible for vernal pools to form.
Vernal pools often fill and empty several times during the rainy season. Only plants and animals that are adapted to this cycle of wetting and drying can survive in vernal pools over time. Vernal pools and the life that depends on them could not exist if it were not for the long history of landscape formation and soil development that created the conditions in which vernal pools can exist. Earthquakes, floods, and volcanoes have all played an essential role in the formation of vernal pools.
These specialized plants and animals are what make vernal pools unique. As winter rains fill the pools, freshwater invertebrates, crustaceans, and amphibians emerge. Vernal pool plants sprout underwater, some using special floating leaves and air-filled stems to stay afloat. Some of these plants even flower underwater! Birds arrive to feed on the vernal pool plants and animals.
California's vernal pools occur on a variety of landscape formations, most often on alluvial formations deposited by ancient waterways and seas. The greatest extent of this type of landscape formation is in our Central Valley, in areas where alluvial surfaces were exposed after the retreat of the inland sea during the Pleistocene era. Similar alluvial landscape formations occur in inland valleys of the inner Coast Ranges, and along coastal terraces of Southern California, where geologic forces have lifted the original alluvial landscape surfaces above sea level.
A second type of landscape formation with vernal pools are ancient volcanic mudflows, where rapid weathering of volcanic materials have formed dense clay soils and bedrock restricting layers near the soil surface. Volcanic landscape formations are found in northeast California and in the northern end of the Sacramento Valley.
Logging requirements:
1) Count the number of different animal TYPES on the plaques at the posted coordinates
2) Take a few moments to examine the soil of the wetlands around the plaque. Describe the consistency of this soil
3) Estimate the length of width of the wetlands in feet
4) Post a picture of you and/or your caching party holding a GPSr
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