Longhurst et al. : Food Interrelationsbips The primary study area The principal study area was the Hopland Field Station, where we have investigated the biology of black-tailed deer and their interrelationships with domestic sheep (Ovis aries) since 1951. This station of over 2,100 ha is in southwestern Mendocino County about 160 km north of San Francisco Bay. Before its acquisition by the University of California in 1951, it was a commercial sheep ranch. The general area has a history of livestock grazing dating back at least to the preceding century. The rangeland on the station is primarily annual grassland, some with an overstory of various species of oaks or other hardwoods, and interspersed with patches of chaparral. A few douglas fir (Pseudotsuga menziesii) trees are present in the more mesic sites. When this study began in 1951, the station encompassed approximately 1,893 ha. Subsequently, in 1954, 16 ha and, in 1965, 259 ha of adjoining public land were acquired from the Bureau of Land Management to give a total of 2,168 ha. Some of the University ownership has not been fenced because of the steep terrain and lack of accessibility. The Hopland Field Station extends from the floor of the Russian River valley to the ridge of the Mayacamas Mountains, where public domain Iandss extend northward from the station. This 22,000 ha-area, which is dominated by dense stands of mixed chaparral, was designated as the Cow Mountain Recreation Area by executive order in 1927. A survey of the vegetational cover types was carried out by Heady and Mallory (1955) on the original field station area, and this provides a good sample of the vegetation present (table 1). TABLE 1.