John C. Reed
2014
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<p>Jefferson County straddles one of the most conspicuous and important geographic and geologic boundaries in western<br/>North America, the eastern flank of the Rocky Mountains. To the east you can travel 1,100 miles across Great Plains and<br/>Central Lowlands before you sight the western foothills of the Appalachians. If you travel in the other direction you will<br/>cross or skirt mountain range after mountain range until you sight the Coast Range near San Francisco, more than 900<br/>miles to the west. Many of these mountains have different ages and origins than the Colorado mountains, but they are<br/>all part of the great mountain belt called the North American Cordillera that extends along the western edge of the<br/>continent from Alaska through Mexico.</p>
<p>What is the reason for the remarkably straight and abrupt eastern flank of the Colorado Front Range? The brief answer<br/>is that it marks the edge of a block of ancient metamorphic and igneous rocks that has been uplifted relative to younger<br/>flat-laying sedimentary rocks that underlie the plains to the east. During the uplift, the sedimentary rocks along the<br/>boundary have been uplifted and tilted eastward to form the discontinuous line of hogback ridges that parallel the<br/>mountain front. Erosion during and after the uplift has removed the sedimentary rocks that once lay above the harder<br/>rocks of the mountain uplift, carved the scenic peaks and mountain canyons in the hard crystalline rocks of uplifted<br/>block, and worn away the softer layers of sedimentary rocks of the plains, but left a few of the harder upturned layers<br/>along the mountain front as hogback ridges.</p>
<p>Jefferson County Open Space Parks, as well as other nearby parks and National Forest lands, offer marvelous<br/>opportunities to explore the geologic story behind this singular landscape. At first the distribution of rocks of different<br/>ages and types seems almost random, but careful study of the rocks and landscape features reveals a captivating<br/>geologic story, a history that tells of the building of the foundations of the continent, the rise and destruction of longvanished<br/>mountain ranges, the ebb and flow of ancient seas, and the constant shaping and reshaping of the landscape in<br/>response to the never-ending interplay between uplift and erosion. This historical account is constantly being improved<br/>and expanded as new evidence accumulates and new interpretations evolve.</p></body></html>
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Trails through time: A geologist's guide to Jefferson County open space parks
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