Southern California’s Anza-Borrego Desert State Park® is a vast, mostly arid desert, but the ancient landscapes of Anza-Borrego were richly populated riparian forests and savanna. Before that, it held a tropical inland ocean teeming with marine life. Today’s eroded badlands provide North America’s most continuous history of life for most of the last 7 million years—one of the richest, most varied fossil records of its time in the western hemisphere—opening windows onto the region’s long-vanished past. Anza-Borrego’s record contains more than 550 types of fossil plants and animals, ranging from microscopic pollen and water fleas to walrus bones and mammoth skeletons, which have been the focus of ongoing research, study, and interpretation since the mid-1850s. The results of the past several decades of study by leading researchers from across the nation can now be seen in this comprehensive work, a compilation of 23 authors each with his own specialty. Early chapters explore background themes and concepts, starting with the Imperial Sea episode. Central chapters present the real stars of the story—individual groups of animals. The bestiary reads like a Who’s-Who of many of the most unique fossil vertebrates on earth—bathtub-sized tortoises, the saber tooth cat, giant ground sloths, the giant short-faced bear, the largest known mammoth, a giant camel, and the largest bird ever to fly northern hemisphere skies. Closing chapters discuss fossil footprints, intercontinental connections, and paleo climates and environmental change in the Anza-Borrego desert region.