The valley's climate is tipically Mediterranean, whit hot, dry summers and cool, moist winters. Rainfall is scant during normal years, averaging only eight inches per year. The topography of the Preserve consists of numerous gently sloping mounds and intervening depressions with a total relief of no more than 10 feet. In the winter, the depressions fill with water, forming from 25 to 75 vernal pools, depending on the ammount of rainfall. During the spring, the vernal pools are bordered by concentric rings of colorful wildflowers as the water in them begins to evaporate.
Amphibians take advatange of the temporary pools in order to breed.
Many of these animals, such as the spadefoot toad, escape summer's heat by burying themselves in the moist soil. By early summer, the pools are dry and many species become dormant to await next year's rain. Most of the plant species are annuals which must set seed before the pools dry completely. The Preserve's mammals include ground squirrels, jack-rabbits and rabbits. Hawks, burrowing owls, and black shoulder kites hunt overhead.