YELLOWSTONE NATURE NOTES

A GLIMPSE INTO THE PAST

Yellowstone has been described as a land of "living geology," a place where the people can see geologic processes in operation. Here one can enjoy the beauty of the landscape and see dramatic evidence of the slow incessant work of water, wind, heat and ice as each has played its part in creating, shaping and altering the land surface. Broad open plateaus, geyser basins, canyons and waterfalls all hemmed in by lofty snow-capped mountain peaks embracing a territory of 3,400 square miles. To the inquisitive park visitor the important question is, "why so much variety in this unique area?"

The answer can in part be found by travelling an imaginary pathway back in time. From astronomic calculations and the radiometric techniques of dating rocks the evidence now points toward a beginning point for the earth some five billion years in the past. Rocks formed since the inception of geologic processes on the earth are recognized within the different eras and periods of geologic time. To place events in their proper perspective we might imagine ourselves travelling backwards in time and walking at such a rate that we cover one thousand years with each pace. Two paces would take us to the dawn of the Christian era, 35 miles to the time when the rocks now exposed on Mt. Everts were being formed, 250 miles to the oldest sedimentary rocks exposed on the Northeast Entrance road, and if we continued the journey covering 1,000 years per pace we would walk in excess of 500 miles to reach the time when the granites of Hell Roaring Mountain were being formed.

Events that took place during these early formative years have been deciphered in the park, but the rocks formed at these times are largely obscured by later geologic formations. The layered rocks of the earth's crust can be compared to the pages of a manuscript, originally bound in proper sequence but later tattered and torn by mountain building processes so that in places entire chapters are missing and others are out of place.

It is the task of the geologist to decipher this jigsaw puzzle and reconstruct past events. Events of the past 70 million years have been most effective in determining the structural framework and topography that we view today and for these reasons we will pick up the sequence at this point.

FIG. 3. Cenozoic History of Yellowstone.
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