FLOOD09509 - Laserfiche WebLink

Home Browse Search

,,",, . . . terrain consists of high, rugged mesas and irregularly surfaced plateaus separated by deep canyons. A web of streambeds and water- ways covers the entire region. Elevations vary from approximately 4 ,500 feet near Frui ta in the northwest, to approximately 9,000 feet in the high mesas in the south, to over 11 ,000 feet in the mountains along the southeastern border. Mesa County is part of the Canyon Lands subdivision of a larger physiographic region known as the Colorado Plateau. Following periods of intense volcanic activity, glaciation, and massive crustal upheavals, during which the basic structure of the Rocky Mountains was formed, evolution of the present land forms of western Colorado began at the close of the Mesozoic era (approximately 60 million years ago). Another broad uplift of the region occurred at that time and, in a following cycle of erosion, vast quantities of rock material were carried away. Following this erosion and surface wasting, layers of sands, clays, and gravels, which are known as the Eocene beds, were deposited over much of the area. Then, a renewal of erosion and the development of a drainage pattern ,on the Eocene beds occurred. It was at this time that the existing main drainage patterns were fixed, and it is since that time that the major topographic characteristics of the county were carved by water and wind. As valleys deepened, the streamways were superimposed on the older, underlying rock. Erosion continued and an old-age erosion surface evolved. The hundreds of plateaus in the region are more or less sharply separated: some rise, table-like, above their neighbors on all sides; others adjoin their neighbors as steps or terraces; and some are basin-like, with surrounding infacing cliffs. They also differ in their degree of dissection by streams; as a result of differing elevations and stages in the erosion cycle, the various plateau formations may differ greatly in temperatures, rainfall, and vegetation. All streams in Mesa County are either direct or indirect tributaries of the Colorado River, which traverses the north- central and northwestern sectors. From the northern county line, the river flows southwesterly for 41 miles to its confluence with the Gunnison River, thence northwesterly 27 miles, and again southwesterly for 15 miles in its remaining course in the county. In general, the Dolores River, Gunnison River, and West Creek systems drain the western, southwestern, and south-central portions of the county. The Plateau Creek system drains the eastern sector, except for the easternmost portion, which is drained by the Divide Creek system, which flows northerly to the Colorado River in Garfield County. A group of minor creeks and washes flowing southerly from the Roan and Book Cliffs regions drain the northwestern portion of the county, and a group of similar streamways convey drainage to the river from the north-central portion. 7