Millions of years ago, the Southwest was a broad plain. During periods of hundreds of thousands of years, the land alternated between shallow seas teeming with primitive life and sun-baked deserts stretching on to the horizon. The seas advanced and retreated, advanced and retreated, each time covering the land with a layer of sediment and silt.
In the periods when the seas receded, the sun and hot desert winds baked the layers and hardened them. Each time the seas retreated,
they left broad watercourses which drained the swampy marshes and in time became the avenues for what little rain fell during the dry periods.
Then, about 70 million years ago, an event of cataclysmic proportions beganΓÇôthe Laramide Orogeny. A powerful surge of molten rock came from deep within the earthΓÇÖs crust and thrust the layers upon layers of sedimentary rocks upward. In some places, the molten rock burst through the sedimentary layers; in others, the layers were bent and tilted. Where the uplifts were concen-
