In a book dense with scientific and historical observations, in which seemingly nothing about the region's flora, fauna, and geology has escaped her notice, Zwinger fashions a joltingly beautiful study of the canyon and its river. The pleasures in reading this book are manifold. Zwinger's (The Mysterious Land, 1989, etc.) quietly heroic accounts of rafting the canyon's 60 rapids are thrilling by themselves, but one also reads of her 19th and early 20th century predecessors' adventuressome fatalon this same water and the types of craft used to navigate the river. Zwinger discusses the pottery, tools, and settlement patterns of the earliest human inhabitants as she floats by or hikes to the many Anasazi sites within the canyon walls. She endures sweltering and bone-chilling days and nights, taking part in eagle counting or tracking of the hump-back chub, now threatened by the changes wrought by the Glen Canyon Dam upstream. Perhaps her most beautiful writing can be found in the minutely detailed descriptions of the insect and reptile life she closely observes, although as occurs around the bends of the river, surprises turn up everywhere in these pages. Zwinger paints vibrant prose pictures of the multicolored canyon walls, expressing a sincere sense of awe at the ancient geologic processes that created and laid down the limestone, sandstone, and basalt flows through which the river cut to reach its present level. On being asked by a tourist, after she hikes up to the canyon rim, whether there is anything ``down there'' to see, Zwinger reflects that `` `down there' encompasses contrasts between minute midge and pounding waterfall, between eternity in an ebony schist and the moment in the pulsing vein in a dragonfly's wing, a delicate shard lost in an immensity of landscape.'' This extraordinary book places Zwinger squarely among the best of today's nature writers.