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Show The frost- free season in the West Colorado Hydrologic Area ranges from less than 20 days in the high mountain areas to more than 200 days in the Lake Powell area. Ecology Like all areas in the mountainous West, the West Colorado Hydrologic Area shows from its lowest elevations to the summit of the high plateaus a vertical succession, or belt, of plant associations. The elevation at which these associations occur depend on such factors as latitude, exposure, soil, and moisture, while the width depends on the steepness of the slope. Comparing the maps and discussions of this section with the previous presentations on topography and climate will help the reader to visualize this correlation. Plants and wildlife communities in combination are often described in terms of life zones. The correlation is imperfect as many species of birds and animals range widely ( at least seasonally) and are found in several plant associations. In fact, otjjfen the most productive wildlife areas are the zones where two or more major vegetal types join or intermingle.^ Nevertheless the use of life zones is useful in understanding the region. Four major life zones occur in the West Colorado Hydrologic Area; they are the Lower Sonoran, Upper Sonoran, Transition, and Boreal. Figures 9 and 10 and the accompanying table depict these zones, the various plant communities within them, and other relationships. Classification of Streams Each stream or section thereof was rated numerically for aesthetics, availability and productivity ranging from 1 to 5. This value is then multiplied by a factor of 1 for aesthetics, 2 for availability, and 4 for productivity. The subtotals are then added to obtain a composite rating, which is used to assign a water to a class. Classes range from Class I, the best fishing waters, to Class VI, the poorest. In the West Colorado Hydrologic Area there are 1,019.3 miles of stream that have been classified by this method. Streams have been segmented where significant physical or ecological changes occur. Figure 11 depicts these streams and their class numbers. The table below shows the number of miles of each class of stream in the West Colorado Hydrologic Area and the State of Utah. Class Class Class Class Class Class 1 2 _ J 4 5 6 Total 0 35.8 330.9 274.4 327.5 50.7 1019.3 61.8 450.9 2522.1 1530.1 645.3 266.7 5376.9 Arable Land There are approximately 232,600 acres of arable land in the West Colorado Hydrologic Area. At present about 85,500 acres are irrigated. There is no dry farmed land in the West Colorado Hydrologic Area. The land that is not cultivated is considered potentially irrigable and includes about 147,100 acres. These lands are shown on figure 12. Mean Annual Runoff Stream flow measurements alone are not sufficient for determining the total natural water resources of an area. In addition, many of the smaller streams which are characteristic of water producing areas are not measured. In order to provide a basis for determining runoff from ungaged drainage areas the water yield or runoff West Colorado Hydro. Area State of Utah |