PERMFILE117348 - Laserfiche WebLink

Home Browse Search

in the vicinity of the proposed Kannah Creek borrow. If any rare plants were discovered, they were to be marked by flagging, plotted on a base map, and subsequently removed to a protected area by a cactus specialist prior to development on the Property. GEOLOGICAL SUMMARY Western Colorado is an area of numerous mountain ranges and broad upwarps (such as the Uinta Mountains, Gore Range, Park Range, White River Plateau, Sawatch Range, Elk Mountains, West Elk Mountains, San Juan Mountains, and Uncompahgre Plateau) separated by downwarped areas ofvazious sizes (including the San Juan basin, the Central Colorado basin, and the Piceance Creek basin). The Kannah Creek Property lies along the boundary between the northwest-trending Uncompahgre structural uplift and the adjacent Piceance Creek structural basin. Rocks present in this area range in age from Precambrian to Tertiary (Fig.3); and they are covered, in places, by unconsolidated Quaternary deposits. Precambrian rocks, some as old as 1.68 billion years, are igneous and metamorphic types. They aze overlain by Mesozoic and Cenozoic rocks aggregating about 15,000 feet. There have been at least three periods of mountain building in western Colorado in its recorded geologic history. The latest began about 65 million years ago at the end of the Cretaceous Period (and the Mesozoic Era) and ceased in the Miocene Epoch (mid- Tertiary). This was the deformation which produced the Uncompahgre upwarp and the Piceance Creek basin. During and following the mountain building, stream and glacial erosion have partly reduced the high areas, such as the Uncompahgre uplift, and removed many cubic miles of the ofd rocks by carrying them into the basins and even to the sea. As a consequence of the erosion, Precambrian rocks have been exposed in the canyons cut deep into the Uncompahgre uplift; and over the rest of the uplift most of the weaker covering sediments have also been stripped off down to the quite resistant Dakota Group of Early Cretaceous age. Weaker sedimentary units, such as the Maness Shale, Mesaverde Group, Wasatch Formation, Green River Formation, and Uinta Formation, have been eroded from the uplift but still form broad valleys and impressive cliffs (Book Cliffs and Roan Cliffs) to the north and east. One of the most recent episodes of erosion in this area was during the Pleistocene or Ice Age (1.6 million to I 1 thousand years ago}. Ice caps on Grand Mesa to the east and on The Uncompahgre Plateau to the west of the study area contributed great volumes of melt water and rock debris to the valleys of the Gunnison River and Kannah creek. At least four stages of glaciation can be recognized here, primarily by outwash terraces at several levels along the valley sides. The last outwash deposits on Kannah Creek fill the valley bottom and are covered by six or more feet of soil. It is this valley fill that will be removed from the Kannah Creek barrow. -2-