Rocks That Shape the Enchanting Landscape
by Frank E. Kottlowski
“As old as the hills.” How much more ancient can anything be? Yet New Mexico’s hills, its enchanting landscapes, were built in but the most recent “minute” of geologic time. Merely one geologic era ago, marine waters covered the state, and storm-tossed waves ruled where now the hot sun beats down on dry sands and cacti a mile above sea level.
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.