During 1921, I spent several months in Baja California determining 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 southward 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 Muleg6 to La Purisima, and in the La Paz region (Fig. i). 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.