312 



Economic Aspects 



Figure 239. Landslide of April 1958 at Pacific Palisades west of Santa Monica which cut off coastal traffic for several 

 weeks. It occurred just as a previous sUde (to its left) had been nearly cleared up by dumping along the shore. Move- 

 ment was so unexpected that it caused one death and the destruction of several pieces of earth-moving equipment. 

 Compare with Figure 20, Section 7. Photograph by Pacific News Pictures. 



creasing rate. Escape of water at the base 

 of the sea cHffs is noticeable at many places, 

 carrying with it the certainty of renewed 

 movement. 



Fewer and smaller slides characterize the 

 other two areas where highways lie at the 

 foot of sea cliffs. West of Point Dume (Fig. 

 20, Section 6) many of the rocks are well 

 consolidated, and the scarcity of residences 

 has protected the area from excessive water- 

 ing. Between Dana Point and San Clemente 

 the cliffs are very steep and consist of poorly 

 consolidated shales and mudstones of the 

 Capistrano formation (Late Miocene or 

 Early Pliocene). Fortunately the dip here is 

 landward, so that most of the movements 

 have taken the form only of rock falls that 

 do not destroy the highway and menace 



only an occasional motorist. With the con- 

 tinuing development of the cliff top as a res- 

 idential district and the consequent water- 

 ing of lawns, larger slides here may well 

 occur. 



In addition to blocking highways land- 

 slides have caused a huge destruction of res- 

 idential property in southern California, 

 and an even larger future destruction can be 

 predicted. In the area immediately west of 

 Santa Monica at least fifteen residences 

 have been destroyed by movements along 

 the sea cliffs and along the sides of valleys 

 incised into them. As pointed out by Mc- 

 Gill (1954), these slides have been promoted 

 by improper excavation and by building 

 atop or below loose fill. Excessive watering 

 of lawns, seepage from septic tanks, leakage 



