From 1920 until his death in 1962, consciousness and its effect on humanity and the natural world was Robinson Jeffers's obsession. Understanding and explaining the biological basis of mind is one of the towering challenges of modern science to this day, and Jeffers's poetic experiment is an important contribution to American literary history--no other twentieth-century poet attempted such a thorough engagement with a crucial scientific problem. Jeffers invented a sacramental poetics that accommodates a modern scientific account of consciousness, thereby integrating an essentially religious sensibility with science in order to discover the sacramentality of natural process and reveal a divine cosmos. Inventing the Language to Tell It traces Jeffers's creation of the poetics that expresses his sacramental-materialist vision, and it proposes that this poetics stands in contrast to modernism by its refusal to divorce mysticism from science. The tension between materialism and mysticism, oppositional powers harnessed together to achieve a unitary purpose, is the cardinal indicator of his sacramental poetics. This study examines this tension as it runs through his work, charting the initial struggle the poet had with accommodating consciousness to his sacramental materialism and detailing the gradual shift to an understanding of the biology of mind. There is no other study of Jeffers or sacramental nature poetry like this one. Jeffers's importance as a sacramental poet was firmly established by Robert Brophy and William Everson, both of whom examined Jeffers's poetry through archetypal psychology and myth-ritual criticism. In contrast, this book proposes that Jeffers's sacramentalism emerged out of his scientifically-informed understanding of material nature. Drawing on ecocriticism, religious studies, and neuroscience, Inventing the Language to Tell It demonstrates how Robinson Jeffers produced the most compelling sacramental nature poetry of the twentieth century.