_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.