thought of as ancient. They are still in the process of building and eroding, and no one today can calculate what they will look like ten million years from now. They have the extravagant beauty of youth, the allure of adolescence, and they are mountains to be loved.
Their history is reasonably clear. Not all were born as a result of basement block uplift, for certain mountains were squeezed upward by vast forces acting laterally. Others may have arisen as a result of some movement of the American plate. And we have visible proof that some of the southern mountains were built by spectacular action.
About sixty-seven million years ago volcanic activity of considerable range and intensity erupted throughout Colorado. As the mountains rose, the crust cracked and allowed lava to rise to the surface in great quantity. Lava flows were extensive, but so were explosions of gaseous ash, which sometimes accumulated to a depth of several hundred feet, compressing itself finally into rock which still exists.
Especially awesome were the vast clouds of gaseous matter which drifted eastward, with internal temperatures rising to thousands of degrees. Whatever they passed over they killed instantly through the exhaustion of oxygen, and when their temperatures fell, the clouds fell too. Their contents then solidified to form crystalline rock, one cloud producing enough to blanket large areas to a depth of seven or eight feet. In other areas, lakes were formed, dammed by lava flows from volcanic fields.
Now for the first time we come to the river which will command our attention for the remainder of this story. It was born coincident with the rise of the New Rockies, called into being to carry rainfall and melting snow down from the heights. For millions of years it was not the dominant river of the region; in fact, five competing rivers led eastward from the Rockies, their long-abandoned courses still discernible in the drylands. They lost their identity because of a peculiarity; an arm of our river began to cut southward along the edge of the mountain range, and in doing so, it captured one after another of the competing rivers, until they no longer ran eastward as independent rivers but coalesced to form the Platte.
When the Rockies were younger, and therefore higher than now, the river had to be of a goodly size. We can deduce this from the amount of material it was required to carry. The area covered by its deposits was about three hundred and twenty miles long and one hundred and forty wide. Depending upon how thick the overlay was, the river had to transport more than seven thousand cubic miles of rubble.
In those early days it was wide and turbulent. It was capable of carrying huge rocks, which it disintegrated into fragments of great cutting power, but its main burden was sand and silt. Its flow was irregular; at times it would wander fifty miles wide across plains; for long periods it would hold to one channel. During these years it labored continuously at its job of building the plains of middle America.
About forty million years ago the building process was aided by a cataclysmic event. To the southwest a group of volcanoes burst into action, and so violent were their eruptions, volcanic ash drifted across the sky for half a thousand miles, held aloft by great windstorms. The ash, blackening the sky as it passed, blanketed the area when it fell. Perhaps at some point an entire volcano may have exploded in one super burst, commanding the heavens with its burden of fire and lava; eruptions continued over a period of fifteen million years, and the wealth of ash that fell upon Colorado accumulated to a depth of thousands of feet. Combining with clay, it formed one of the principal rocks of the region.
It is difficult to comprehend the violence of this period. Twenty-three known volcanoes operated in Colorado, some of them much larger than Vesuvius or Popocatepetl. Obviously, they could not have been in constant eruption; there
Their history is reasonably clear. Not all were born as a result of basement block uplift, for certain mountains were squeezed upward by vast forces acting laterally. Others may have arisen as a result of some movement of the American plate. And we have visible proof that some of the southern mountains were built by spectacular action.
About sixty-seven million years ago volcanic activity of considerable range and intensity erupted throughout Colorado. As the mountains rose, the crust cracked and allowed lava to rise to the surface in great quantity. Lava flows were extensive, but so were explosions of gaseous ash, which sometimes accumulated to a depth of several hundred feet, compressing itself finally into rock which still exists.
Especially awesome were the vast clouds of gaseous matter which drifted eastward, with internal temperatures rising to thousands of degrees. Whatever they passed over they killed instantly through the exhaustion of oxygen, and when their temperatures fell, the clouds fell too. Their contents then solidified to form crystalline rock, one cloud producing enough to blanket large areas to a depth of seven or eight feet. In other areas, lakes were formed, dammed by lava flows from volcanic fields.
Now for the first time we come to the river which will command our attention for the remainder of this story. It was born coincident with the rise of the New Rockies, called into being to carry rainfall and melting snow down from the heights. For millions of years it was not the dominant river of the region; in fact, five competing rivers led eastward from the Rockies, their long-abandoned courses still discernible in the drylands. They lost their identity because of a peculiarity; an arm of our river began to cut southward along the edge of the mountain range, and in doing so, it captured one after another of the competing rivers, until they no longer ran eastward as independent rivers but coalesced to form the Platte.
When the Rockies were younger, and therefore higher than now, the river had to be of a goodly size. We can deduce this from the amount of material it was required to carry. The area covered by its deposits was about three hundred and twenty miles long and one hundred and forty wide. Depending upon how thick the overlay was, the river had to transport more than seven thousand cubic miles of rubble.
In those early days it was wide and turbulent. It was capable of carrying huge rocks, which it disintegrated into fragments of great cutting power, but its main burden was sand and silt. Its flow was irregular; at times it would wander fifty miles wide across plains; for long periods it would hold to one channel. During these years it labored continuously at its job of building the plains of middle America.
About forty million years ago the building process was aided by a cataclysmic event. To the southwest a group of volcanoes burst into action, and so violent were their eruptions, volcanic ash drifted across the sky for half a thousand miles, held aloft by great windstorms. The ash, blackening the sky as it passed, blanketed the area when it fell. Perhaps at some point an entire volcano may have exploded in one super burst, commanding the heavens with its burden of fire and lava; eruptions continued over a period of fifteen million years, and the wealth of ash that fell upon Colorado accumulated to a depth of thousands of feet. Combining with clay, it formed one of the principal rocks of the region.
It is difficult to comprehend the violence of this period. Twenty-three known volcanoes operated in Colorado, some of them much larger than Vesuvius or Popocatepetl. Obviously, they could not have been in constant eruption; there
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