26 



University of California. 



[Vol. :i. 



mountains back of the terrace east of Newhall ( which is tilted 

 toward the southwest) to form a detrital slope. The material is 

 clearly river-deposited and not due to ephemeral "cloud-burst" 

 floods. Near Castaic Station the present valley is not quite on 

 the axis of the synclinal trough, but the river passes to the north 

 of it, leaving a fragment of the southwest- sloping terrace on the 

 south of the river. Slight faulting is also apparent near Castaic 

 Station. The deformation was one of depression of the central 

 portion of the trough and not of uplift of its borders. The 

 "400-foot terrace" in the axis of the trough is several hundred 

 feet lower than in the surrounding country where it is undis- 

 turbed except by an uplift general to the whole region. The 

 abnormally broad Newhall V alley is due to the ease with which 

 it was widened by lateral corrasion on the site of this local sag in 

 the "400-foot terrace" plain. Most of the tilting seems to have 

 been affected at about the opening of the Modern epoch but it 

 may have continued later. 



THE LATER QUATERNARY EPOCHS. 



On the basis of erosion studies, I will correlate in a general 

 way the three lower marine terraces of San Pedro Hill, the second 

 Quaternary deposit in the City of Los Angeles, the lower river 

 terrace of Soledad Canon, and the second formation of the Bed 

 Bluff area in the Great Valley. I am inclined also to place in 

 this same category the marine Pleistocene sands resting horizon- 

 tally on the Merced series near Lake Merced on the San Francisco 

 Peninsula. These various deposits may not be strictly contem- 

 poraneous, but they seem to have been the product of a stage of 

 the Quartenary era when there was a tendency of the land to 

 subside, or at any rate, the conditions were those of a land tem- 

 porarily somewhat below its normal level. The silt terraces of 

 Los Angeles apparently indicate a slight depression. The two 

 lower terraces of San Pedro were formed while the land was 

 regaining its normal level. Hence, the silt terraces of Los 

 Angeles may be older than the two lower marine terraces of San 

 Pedro Hill, but the difference in their ages is very, very slight. 

 Deposits of about this age are sufficiently developed in California 

 and sufficiently distinct from an older series and a newer series 



