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C. Topography and 6eolcxJy The Augustin Bernel Park site rests along the crest and on the steep northeast slopes of the Pleasanton Ridge, rising from an elevation of 700 at its base to 1556 feet at its highest peak. The geologic make-up of the ridgelands coupled with its rough topography form one of the most limiting features for development of the site. " The geology underlying the park is a sedimentary formation dating back to the Jurassic and Cretaceous periods, approximately 100 million years ago, and consists predomtnately of cobble conglomerate which is visible in several outcrops along the trails. The upper portion of the park along the ridgeline is characterized by arkssic sandstone, and the southwest corner of the site is composed of b;~ale and minor graywacke sandstone. According to the Geologic Zone map o~ the City o~ Pleasanton, the site is in a geologic zone which is susceptible to a high degree of landslides and seismlc shaking, and a moderate degree of rockfails, erosion, and expansive soils. The lower areas of the site are covered with older landslide deposits composed of massive, poorly sorted debris. The unstable nature of the landslide areas would deter the siting of any major park facilities. The largest ancient landslide in the area known as the Castlewood slide is the site of the Castlewood Country Club. The Calmverse fault is located to the east of the park running from the northwest to the southeast psrellel to the Pleasanton Ridge. The fault, although abecured in places by the landslides, has been active within recent times. In terms o~ site topography, only isolated areas near the top (totalling less than six acres) offer alepea suitable for structures. Access to these areas is limited, however, and would preclude the placement of any significant improvements. The climate of the park is typical for its setting within the rolling constel hllls of the Bay Area. Average annual rainfall is approximately 22 inches. Most rainfall occurs during the winter and spring months with a summer drought. Temperatures can range from a mean low of 40* farenheit to a mean msxlmum of 90'. The dry hot summer weather increases the risk of fire in the park. Hiking the hillside trails during this part of the year can also be strenuous for the average park user. The site supports several snnuml streams whlch carry water only in the winter and spring. A spring which maintains a trlckle of water even in the summer months is located along the main trall. Zts potability has not been tested as yet.