15 ATTACHMENT 9 - Laserfiche WebLink

Project No. 9929.G Geotechuical Investigation/Vineyard Avenue, Pleasanton 8 August 2003 Vegetation on the site is consisting mainly of dense dry grasses and occasional bushes and dense oak trees and some eucalyptus trees. Bared wire fences are present throughout the subject site. This description of the site is based on a reconnaissance by the Soil Engineer and a preliminary development plan by Ruggeri-Jensen-Azar & Associates. Geolol=ic Setting The subject site is within the Coast Ranges geomorphic province, a belt of sedimentary, volcanic, and metamorphic rocks, which extend from southern California to Oregon. The structural geology of the Coast Ranges is complex and dominated by transpressive stress (combined transform and compressional) concentrated along faults within the San Andreas Fault system. On the eastern portion of the San Francisco Bay, bedrock geology consists of sedimentary and metamorphic rocks ranging from Cretaceous through Quaternary periods (up to 144 million years to present). The subject site is located on the northwestern margin of the Diablo Ranges, along the southwestern portion of Vineyard Avenue in eastern Pleasanton, California. According to Majmundar (1991), the site is underlain by Livermore Gravel (Plio-Pleistocene in age) which consists of buff to reddish-gray cobble-pebble gravel containing debris from Franciscan Complex rocks (chert and serpentine). This unit contains scattered vertebrate fossils and landslides in this unit are concentrated along canyon walls or bluff like edges. A questionable landslide feature was mapped on the property by Majmundar (1991), which was mapped as approximately 1,000 feet in length and approximately 400 feet in width over most of the property. Details of the geology and landslide are shown on Figure 1, Regional Geological Map. The Verona and Calaveras Faults are the closest active-faults, situated approximately 3.5 km and 7 km southwest and west of the subject site respectively. The Verona Fault is listed as an active thrust fault by the Alquist-Priolo (AP) Earthquake Fault Zones Act (Division of Mines and TERRASEARCH, inc. Page 7 of 53