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The wetland and floodplain areas of the site are characterized by six major wetland communities. Cooper and Severn (1994b) described these communities as follows: ~ I I I I I I I I I I I I I I I I I I I GeoloQY and Soils The site occurs on an abandoned river meander where the Green River has eroded into an adjacent terrace. The terrace has a bedrock core of Mancos Shale and has a Quaternary alluvium cap of approximately 10 m thickness. The abandonment of this river meander could have resulted from the bedrock of the terrace forcing the river back to the west, natural straightening of the channel, channel incision and the construction of an artificial dike. As a result of the dike being constructed, the natural flooding of the this meander channel and the presence of ephemeral waters caused by overbank flows have been prevented (FLO Engineering 1993). Snowmelt, rain and irrigation water percolate through the coarse- textured alluvium and contact the shale which is an impermeable layer. The water then flows west on top of the shale and erupts as a line of springs on the terrace face. The groundwater leaches salts from the shale resulting in waters with high salt concentrations in certain areas (Cooper and Severn 1994b). The bedrock core appears to extend eastward from the site under the entire peninsula. Thus, groundwater recharge from the east by the Green River is not likely. Soils in the wetland and floodplain areas range from clay loam to peaty loam. Upland terrace~soils range from sandy loam to loamy fine sand. The presence of contaminants within the substrate is likely. Based on water chemistry and vegetative development, soils contain locally high or excessive levels of salts, selenium and nitrates. Veqetation The vegetation on this site has changed considerably from 1937 when the earliest photographs of this site were taken. The site retained its floodplain character until the 1950's, even though it was diked from the river in the late 1800's. The 1937 photo shows that the site contained much bare ground and a large population of cottonwood trees. The development of irrigated agriculture on the terraces to the east of the wetlands created a groundwater flow system into the eastern portion of the wetland. Open water and emergent marshes now occur in this area. The groundwater discharge has created a high water table which supports the extensive marsh system and most likely drowned the cottonwoods. Figure 5 shows an aerial photograph taken in 1987 and represents the current vegetative condition of the site. 10