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-29- Colorado River The applicant identified unconsolidated streamlaid deposits within and adjacent to the proposed permit area which meet the minimum size requirement of 50 feet in width by 10 acres in extent as set by the OSM alluvial valley floor guidelines. These unconsolidated streamlaid deposits border the Colorado River. Three distinct types of unconsolidated deposits were mapped which meet the geomorphic criteria for alluvial valley floors. These deposits are quaternerary terrace deposits, quaternerary transition zone between terrace and colluvial outwash and quaternerary colluvial outwash. The unconsolidated sediments cover approximately 500 acres in the area of the surface facilities between the Colorado River and the Grand Hoghack. Of the 500 acres, 216 acres are colluvial outwash, 136 acres are terrace deposits. Most of the area mapped as terrace and transition zone deposits is presently used for irrigated agriculture. Only a small portion of the area mapped as colluvial outwash is presently used for irrigated agriculture. The source of water for irrigation is the Vulcan ditch which diverts water from Canyon Creek. Canyon Creek is located north of the Colorado River. In addition to the area presently used for irrigated agriculture, two areas exhibited characteristics of subirrigation (Figure 5.2-2). The largest area is adjacent to the Colorado River. The source of the water for subirrigation of this area is most likely the Vulcan ditch, since the area is approximately 20 feet above the level of the Colorado River. The only other area exhibiting subirrigation is in a small ephemeral drainage. This area is split in half by the Vulcan ditch. The only possible sources of water for irrigation of the areas identified as unconsolidated sediments are Canyon Creek, the Colorado River, and South Canyon Creek. All the area below the Vulcan ditch can be irrigated with water from Canyon Creek, therefore, this area meets the water availability criteria for an AVF. Water from Canyon Creek cannot be used to irrigate the unconsolidated sediments above the Vulcan ditch due to the physical barrier of elevation differences. In order to irrigate the remaining area from South Canyon Creek and the Colorado River, over 9 and 14 miles of ditch, respectively, would have to be constructed over extremely steep terrain. Water from the Colorado River would have to be diverted in Glenwood Canyon and the ditch would have to be Constructed through Glenwood Springs. It is not the regional practice to divert water over extremely rough terrain, therefore, the area above the Vulcan ditch does not meet the water availability criteria for an AVF. The exception to this is the subirrigated area above the Vulcan ditch. Based upon the above discussion, the Division has determined that all the area underlain by unconsolidated streamlaid deposits below the Vulcan ditch plus the small subirrigated area above the Vulcan Ditch is an alluvial valley floor. For reference, the alluvial valley floor includes all the area denoted as: 1) land presently flood irrigated; 2) land historically flood irrigated; and 3) areas of probable sub-irrigation, as shown on Figure 5.2-2 of Volume V of the application.