This guide provides a needed resource for the mammals occurring in southern California and portions of the eastern and southern Sierra Nevada in one volume. The 150 species accounts provide a brief discussion of each species' taxonomy, distribution, and ecology. Like no other recent book on the mammals of this area, this guide provides a breakdown of each species by subspecies and their distribution on a colored map that accompanies each species account. This guide provides a summary of the laws and regulations pertaining to mammals and in each species account the laws and regulations pertaining to that species are provided. The introductory chapters include descriptions of vegetation communities and their dominant plant species, which should be useful in determining the occurrence of a species at any particular site. This book fills a gap in our knowledge of mammals in the guide area and is meant to be used by interested amateur naturalists, recreationalists, and professionals. Toward that goal this book has used language that is not so technical as to be lost on the non-scientist, but technical enough to be of use to scientists, and professional biologists. Lastly, this book is meant to stimulate further research into mammals in the guide area.