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, " I :1 ,I " I Ii Ii ,I 'I :, ;1 , ,I " , , I; :, .~. " !I " " , " il , 'I . ", . '\. o {I 005'; --------- - ,--------- -17- less pervious than the gravel and sand found in the deep channel. This is due to the difference in deposition conditions. Thc upper flood plain channel was deposited by a relatively slow moving, meandering, braided river which spread over a wide arca and deposited both fine and coarse grained sediments. The lower inner channel had a faster flow in its more restricted channel aud deposited cleaner and coarser material. The sand and gravel in the deeper channel is much more pervious than the Uppel' level sedimen ts. However, being covered by the less pervious alluvium, it does not present as ser ious a seepage prob lem as it might otherwise. Our seepage studies are discussed elsewhere in this report. Neither the upper or lower channel contains large cobbles or boulders. The overburden along the higher parts of the proposed axis is primarily a mixture of dune sand and loessial silt. It is poorly consolidated and shows little evidence of cementation. The lac!, of a water table in the drill holes in this layer in- dicates that what precipitation falls on it apparently drains to- ward the river and docs not maintain a water table. The area .of the old, wide, rivel' flood plain overlies river sand and gravel. On the higher abutments it lies directly upon bedrock. When exposed to reservoir saturation, this material is expected to slump and settle to considerable extent. In placing a spillway at the lower Weld County site, it is likely that the designers will choose to place it on bedrock. The drilling indicates that this could be done on either abutment; ,I '[ however, the right abutment appears the most feasible. In comparing [;eologic conditions at this site to the Narrows " ." ..-,.