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-zz- The faults in the Hayden Syncline may provide a vehicle for ground water communication between overlying and underlying aquifers and also between aquifers and the overlying surface streams. The faulting produces increased fractures within and between aquifers (secondary porosity). These more porous fault zones with their higher permeabilities can control both vertical and horizontal movement of ground water between and within aquifers. In areas where hydrostatic heads are higher in the underlying aquifers than the overlying surface elevation or the hydrostatic heads in overlying aquifers, the vertical movement of water through the fault system would be upward and discharge to the surface system or recharge overlying aquifers. The lenticular and interbedded sandstones associated with the coal bearing zones develop only localized discontinuous aquifers. Movement of ground water within these sandstones is usually localized, with the flows of water from the recharge to the discharge area occurring within a short distance. Some limited regional movement of ground water may occur if there is intercommunication between the sandstones. The recharge, discharge and movement of ground water within the alluvial aquifers are controlled by: 1) the gradient of the rock channel into which the alluvium has been deposited, 2) the width of the alluvial deposit, 3) the thickness of the alluvial deposit, 4) the permeability of the alluvial deposit, 5) the recharge or discharge of underlying rock strata, and 6) the flow characteristics of the associated stream. The alluvial ground water aquifers are closely related to their associated streams. The alluvial aquifers receive a majority of their recharge from the stream and sustain baseflows in the streams through their discharge. Recharge to aquifers occurs primarily in the spring and early summer when snowmelt and surface water runoff is abundant, and when transpiration by vegetation and evaporation is at a minimum. Recharge to rock aquifers is limited by the permeability of rock strata and the limited recharge area exposed to surface water (e.g. most sandstones are cliff formers). Overlying clayey and silty soils, and shale and siltstone rock strata also limit vertical recharge of underlying sandstone and coal aquifers. Discharges from bedrock strata are primarily through springs to the surface system. The flow characteristics of the springs are related to 1) the lateral extents and thicknesses of the associated aquifers, 2) the distance between the springs and the aquifer recharge areas, and 3} the permeabilities and ground water storage characteristics of the associated aquifers. Springs issuing from laterally discontinuous, thin sandstones (lenticular and interbedded sandstones} which occur close to the aquifer outcrops often flow intermittently and their flows tend to fluctuate seasonally. Springs issuing from regionally extensive, thick sandstones or coals flow perennially and their flows do not significantly fluctuate with time.