74 POPULAR SCIENCE MONTHLY 



other evidence that there has been sudden slipping along these fault 

 lines in very recent years, comparable in importance with movements 

 of two months ago, especially as expressed in fault scarps ? According 

 to the preliminary report of the earthquake committee, the rupture of 

 April 18 shows a horizontal displacement averaging 10 feet, and a 

 vertical displacement not to exceed four feet. How long such a sur- 

 face disturbance can be subsequently recognized is a question. The 

 San Andreas fault belt is well situated for the noting of any such dis- 

 placement for several miles southeast of Mussel rock, in many cases 

 the actual fault planes emerging in sublevel pasture land at the sur- 

 face. Neither the writer's notes nor his memory now yield any evi- 

 dence of such a scarp. On the other hand, the fact that where such 

 evidence might be seen has long been subject to the tramping of cattle 

 renders its absence of less value. In this connection he does not give 

 any value to a small scarp noted just back of Mussel Rock. At the 

 time, it was considered to be a land slip. A photograph taken of it 

 suggests the possibility of its having a deeper meaning. 



But if such scarps are lacking, there is abundant evidence of another 

 kind bearing on this subject. I have spoken of the San Andreas fault 

 belt. Such it appears to be rather than a single clearly-defined break. 

 Along this belt between San Andreas lake and where the belt meets the 

 ocean at Mussel Rock is a string of drainless depressions occupied with 

 water part or all of the year. In one or two cases these can be clearly 

 seen to lie directly in one of the lines of faulting. That they are the 

 result of fault movements seems highly probable. When were they 

 made? That they were made within the last few centuries can not be 

 asserted, yet the fact that so many of these shallow basins still exist, 

 neither filled nor drained, notwithstanding that in many cases it is but 

 a stone's throw to the head of a drain with a high gradient, suggests 

 such a possibility. The possible cause of these basins is suggested in 

 what appears to have formerly been one, now trenched from two direc- 

 tions at the head of Wood's Gulch, a small ravine cutting the cliffs 

 of Seven Mile beach, a mile north of Mussel Rock. The ravine follows 

 a fault with downthrow of 800 feet. At the head a cirque-like cut 

 exposed an overhanging fault scarp of 100 feet or more. Against this 

 face there appears to have gradually filled in wash from the adjacent 

 hills, wind-blown sands and detached fragments from the fault face, 

 until the whole thing was buried and later covered with the marine 

 deposits of the last submergence. Judged from what is left of this 

 filling, it must at one time have strongly resembled the undrained 

 basins just described. The evidence suggests that this fault scarp 

 was produced by a single movement. An elephas tusk found about 



75 feet from the top of the filled in deposit agrees with the other evi- 

 dence in placing the time of this movement back to the land period 

 preceding the recent submergence. 



