RES 94118B - Laserfiche WebLink

Project No. 5541 1 lune 1993 OAK TREE FARM GEOLOGIC HAZARD ABATEMENT DISTRICT CGHAD") PLAN OF CONTROL PLEASANTON, CALIFORNIA 1.0 l.l 1.2 C.,eolo~ic Setting The boundaries of the proposed Oak Tree Farm Geologic H~7~rd Abatement Dis~ct CGHAD") are shown in the legal description and the map attached as Exhibit A and Exhibit B respectively, to this Petition for Formation of the Oak Tree Farm GHAD. The district is located along the foothills of the Sunol Ridge on the west of Foothill Road in the City of Pleaseaton. The northeasterly third of the parcel is nearly flat valley bottom land, the remainder of the site is undeveloped hillside which generally slopes to the east cad contains a series of seasonal incised drainages. This slope is highly irregular with inclinations ranging from 8:1 (horizontal to vertical) to 1:I. Relief on the site is a maximum of 330 feet with elevation ranging from 185 feet on the southeast edge of the property to 615 feet on the southwest comer. The proposed development area encompasses the entire ~a~ead along Foothill Road plus a number of custom lots on the bonom portion of the hillside. The hillside portion of the site is composed of extensive ancient leadslide deposits. The deposits are up to about 50 feet in thickness. Underlying the old leadslide deposits and outcropping at the bottom of the hillside area, are masine ead non marine sedimentary rocks. The older of these rocks are Miocene Age, folded, marine siltstones ead sandstones. Overlying the marine sediments are terrestrial, Plio-Pleistocene Age, mostly clayey gravel deposits. The castera fiat lying portion of the site consists of deep valley alinvium composed of unconsolidated, mixed, silL, sand, clay, earl some gravel. 2.0 Dascrivtion of Geolo~tic H~'~rds 2.1 Beesuse the eastern fiat lying portion of the site, which is the primary development area, is distinctly different from the moderate to steeply sloping hillside area on the west, geologic baT~rds which affect the site can be separated for the two topographically defined areas. The hillside area consists primarily of leadslide deposits. Three types of leadslides are delineated on the basis of surface features, The first type, termed "active" landslides, 2 EXHIBIT__C__