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f -4- The proposed permit area lies on the eastern flank of the Twentymile Park Structural Basin. The basin is a synclinal extension of a much larger basin, the Washakie-Sand Wash Structural Basin. The syncline forming the basin is a doubly plunging, north-south trending syncline known as the Twentymile Park Syncline. The only major structural feature in the area is a 200 foot wide fault zone. The zone lies to the west of the proposed permit area and trends northwest - southeast. It has a normal type displacement of 60 to 100 feet. Four geologic formations exist in the vicinity of the Fish Creek tipple. They are, in ascending order, the Mancos Shale, the Iles and Williams Fork Formation of the Mesaverde Group, and the Lewis Shale Formation. These strata were all deposited during the late Cretaceous Period. Generally, the strata Dip to the west at 8o to 14o into the Twentymile Park Basin. Three mineable coal seams, the Lennox, Wadge, and Wolf Creek Coals, are located within the Williams Fork Formation. The Wadge coal has previously been mined and the area reclaimed within and adjacent to the permit area. No mining is proposed as part of this permit application. Three regional bedrock aquifers underly the permit and adjacent areas. These aquifers are the Trout Creek Sandstone, the Twentymile Sandstone, and the Wadge coal-overburden zone. No further disturbance of these aquifers is planned as part of this permit. The alluvia of Trout Creek and its tributaries are also important sources of ground water. The alluvial bodies are used as water supplies, provide subirrigation to vegetation and supply base flow to the streams. The alluvial bodies are recharged by both the streams and the bedrock aquifers. The two alluvial aquifers within the permit boundary are the Fish Creek alluvium and the Middle Creek alluvium. Middle Creek does not receive significant water from the bedrock ground water system. Most of the water in this aquifer is from surface runoff. The alluvium of Fish Creek receives water from both the underlying bedrock aquifer and surface water infiltration. Climatic conditions in the area are typified by heavy snowfall and cold temperatures in the winter months and moderate summertime temperatures. Freezing temperatures can occur during any month of the year resulting in a short growing season. Average annual precipitation is approximately 16 inches. Less than 20% of this occurs during the growing season months of June, July and August. Vegetation in the vicinity of the tipple is characterized by four major vegetation types: Pastureland, Alkali sagebrush, Meadow Hay and Brome Hay. The pastureland vegetation type is the dominant type and it is found throughout the permit area on a variety of slopes and aspects. It is dominated by big sagebrush and snowberry. The understory is dominated by wheatgrasses and arrowleaf balsamroot.