Early settlers grazed cattle and sheep, but soon farming became the dominant activity in the valley. In order to ensure the permanent preservation of the pools, Mr. Zinanovich transferred the property to The Nature Conservancy in 1964. In 1986, the U. S. Department of Interior gave it the designation of National Natural Landmark in recognition of its unique botanical values. During the summer of 1997, the property was transferred to the Center for Natural Lands Management. 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.