GEOLOGY. 
49 
of solfataras and have given rise to the opinion that volcanic activity 
is present in this region. This so-called “Rincon volcano” existed 
before 1855, being referred to in the Pacific Railroad reports; this 
shows that the burning has continued a long time. 
TYPICAL OCCURRENCES OF BURNT SHALE. 
Outcrops of burnt shale occur in eight or ten localities in the Santa 
Maria district. The best examples are at various places along the 
ridge of the Casmalia Hills from a point south of Schumann to 
Waldorf; on the north and south sides of Graciosa Ridge; and on 
Redrock Mountain 4 miles southeast of Los Alamos. In each of 
these regions every stage of alteration is exhibited, from the slightly 
discolored shale to hard slaglike rocks of varying shades of red and 
black. The area of altered shale in the different localities ranges 
from about a hundred square feet to a half a square mile or more, as 
at Redrock Mountain. In each the burnt rock is surrounded by unal¬ 
tered, usually soft, white, diatomaceous shales which in most places 
show the planes of stratification. At no point observed was a sign 
of stratification left in the baked shale. In every occurrence the shales 
in the neighborhood are bituminous and asphalt deposits are usually 
adjacent. 
The largest area of altered shale is on the summit and surrounding 
ridges of Redrock Mountain. This is the highest of the hills in the 
basin region between the San Rafael and Santa Ynez mountains, 
being 1,968 feet above the sea; the height of most of the summits in 
the vicinity is from 1,000 to 1,500 feet. Redrock Mountain seems to 
owe its prominence, at least in part, to the metamorphosed shale that 
forms its summit. Likewise, in the 800-foot hill on the southeast side 
of Schumann Pass, the capping of this same character, resembling 
volcanic rock, seems to have caused the topographic relief. The 
metamorphism in these localities probably took place a long time 
ago. At Redrock Mountain great deposits of asphalt are in places 
in contact with the altered shale, and there is a large area of shale 
impregnated with bitumen. 
DEPTH TO WHICH ALTERATION HAS EXTENDED. 
The depth to which alteration has extended below the surface in 
these occurrences is difficult to determine. A cliff of burnt shale 
50 to 100 feet high is exposed 4| miles due south of Guadalupe, and 
the difference of elevation of points in the Redrock Mountain neigh¬ 
borhood where the altered rock outcrops amounts to several hundred 
feet. That such metamorphism of the shale has not been solely a 
surface phenomenon is shown by the fact that burnt shale has been 
found at considerable depths in drilling. Mr. Orcutt, of the Union Oil 
Company, exhibited samples of red shale, coming from depths of 950 
