GEOLOGIC RECONNAISSANCE IN BAJA CALIFORNIA 
N. H. DARTON 
United States Geological Survey, Washington, D.C. 
During 1921, I spent several months in Baja California deter- 
mining geologic relations of a large area, and as there is but little 
on record regarding the geology of this region, it is desirable to 
set forth such of my observations as appear to be of general 
interest. I journeyed with pack train from near Ensenada south- 
ward to beyond Comondu and later extended the reconnaissance 
to beyond La Paz as far as Todos Santos. Most of the observations 
were in the district between the high sierra and the west coast, 
but the peninsula was cross-sectioned near San Ignacio and Santa 
Rosalia, from Mulegé to La Purisima, and in the La Paz region 
(Fig. 1). 
Most of my attention was given to the sedimentary rocks of 
Cretaceous and Tertiary age, but the limits and character of some 
of the crystalline rocks were ascertained. Many of the general 
relations are set forth in the cross-sections of Figures 2, 3, and 4. 
PRE-CRETACEOUS 
The lowest strata observed were schists and other metamorphic 
rocks, invaded by white, massive, coarse-grained granite. At most 
places this granite includes fragments of schist, and many clearly 
intrusive contacts were noted. The granite constitutes the high 
Sierra San Pedro Martir in the north central part of the peninsula, 
where one or two summits reach an altitude of about 10,000 feet. 
It also outcrops north of Ensenada, north of Santa Caterina, and 
in many high central ridges from latitude 29° 30’ to latitude 28°, 
and is prominent in the sierra at the lower end of the peninsula 
southeast of La Paz. I crossed the schists in several broad zones 
between Santa Caterina and Calmalli and noticed that a few miles 
720 
