Laserfiche WebLink
200 fee[ high. Two small features (Ls3) indicative of active movement were noted, both located <br />• on the lateral boundaries of the ancient slide mass. A recent rotational slump of about 1/4 acre, <br />with a head scarp of about 12 feet was noted on the side slope of the large landslide about 250 <br />feet southwest of Boring 7. This feature occurred less than 2 years ago, and was probably the <br />result of slope strength loss on the oversteepened side slope. We could not access the face or <br />toe of the slump due to vegetation and difficulty traversing the slope. No tension cracks were <br />observable above the tteadscatp. The drainage side slope in the area was measured at between <br />1 and 1.6H:1V. Another feature, a relatively small earthflow type slide in the axis of the <br />drainage above Boring 11 was noted. This shallow slide appears to be actively creeping <br />downhill, and has moisture seeping from the toe, particularly at the east side. This slide may <br />be moving because of a ground water level increase in the drainage area due to the large rock <br />slope failure above and to the east of the portal area. Another small seep was noted 400 feet <br />• west of Boring 21. <br />The soil and bedrock units are not expected to respond unusually to seismic activity. The <br />area has been classified as a Zone 1 Risk Area that can expect only minor damage from <br />earthquakes of intensities V or VI on the Mercalli Scale. Maximum bedrock accelerations at 4 <br />percent of gravity are probable during major earthquake events in the area. <br />Erosion potential is low to moderate across this site, due to steep slopes, thick to sparse <br />vegetation and silty clay soils. Erosion potential may be expected to increase somewhat during <br />construction, but should return to pre-construction rates, or less, if proper construction and <br />grading practices are followed. <br />7 <br />