From the end papers:
People of all cultures, from nomadic hunter-gatherers to settled agriculturists, have been awed by the creative principle and have expressed this in their art. Humankind's efforts to understand the great mysteries of birth, death, and sexuality have inspired graphic images and vivid mythologies. Although the meaning of many petroglyphs and pictographs is a mystery, fertility has been identified as one of the most obvious and pesristent themes in rock art of prehistoric cultures in the Southwest and around the world. These images suggest that their ancient creators were concerned with appeasement of supernatural forces to ensure their procreant forces continued to sustain their lives. In addition to the obvious desire for successful reproduction of the people, their concerns extended to the fertility of earth itself and the fecundity of plants and animals -- the community of life upon which physical and spiritual well-being depended.
In the context that much rock art is thought to be sacred and tied to the religious beliefs of the cultures that made it, notions of fertility, abundance, and creation are imbued with spiritual potency and special significance. Thus we find in the rock art record of the Southwest not only images of human sexuality and reproduction but a wide array of related images spanning the natural and cosmic worlds. The Serpent and the Sacred Fire records pregnant game animals and successful hunts; seeds and edible plants both wild and cultivated; symbols of rain and of supernatural beings upon which all depends; and depictions of sexual rituals intended to ensure a fruitful earth.