What determined the Land of Enchantment’s landscapes? Shaping these land forms are the rocks of the earth’s crust, the structure of those rocks, and the endless battle between the rocks and the atmosphere. A story spelled out in stone, the geologic history. The rocks determine. Eons ago, it began; one billion, two billion, or perhaps even more billions of years ago. A history whose beginnings have been lost owing to destruction of its earliest records. A history, written in the rocks, that is divided into four general parts (fig. 1). The oldest rocks, more than 600 m.y. (million years) old, almost devoid of traces of life, are the Precambrian rocks. The Paleozoic rocks, 230 to 600 m.y. old, are marked by ancient (_paleo_-) life. This was the Period of Invertebrates, animals without backbones. Mesozoic rocks, 70 to 230 m.y. old, formed in the Era of Dinosaurs and contain types of life that are intermediate (_meso_-) between the ancient and modern animals. And rocks of the Cenozoic Era, 70 m.y. ago to the present, make up the latest (_ceno_-, recent) chapter of the earth’s history. Events of the Cenozoic Era have had the greatest influence on New Mexico’s landscapes. So let us begin the story at the dawn of the Cenozoic, and return to the earlier geologic chapters later. CENOZOIC ERA The mountains, the plains, the rivers, and the lakes all are transitory features of the landscape, created during the recent part of the Cenozoic Era, and all doomed to destruction in the near future, geologically speaking. Even so, some of the plains and mountains may predate man’s evolution onto the earth scene. Gone were the late Mesozoic seas; never again during our lifetime nor the lifetime of many future generations will marine waters roll over New Mexico, and sea-spawned creatures rule. For the first two thirds of the Cenozoic, the Paleogene Period (25 to 70 m.y. ago), New Mexico suffered from the dying effects of the great Laramide upheaval of the earth’s crust. Large areas were exposed to the harsh erosion of stream and wind. The landscape looked as parts of southwestern New Mexico do today—tall rugged mountain ranges scattered in isolated patches amid wide gravelly plains. But the climate was more humid, and while no large through rivers are known, local great swamps and lakes lay on the plains in debris-trapping lowlands. [Illustration: Figure 1. Table of geologic time] _Scale of geologic time in millions of years_ _Era_ _Rocks_ _Dominant life_ _Geologic age_