Southern California is a region of great geologic and topographic diversity. The land in this region may be divided into four natural landform areas or provinces, mainly based on distinctive physiographic characteristics. This monograph will concern itself only with a portion of two of these natural regions: the Colorado Desert Province and the Peninsular Ranges Province. The geographical characteristics to be considered for this area are geomorphology, climate, soils, biogeography, and human presence. Special emphasis shall be given to the description of those physical phenomena which help relate the story of early man in the area.