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;'J 1421 Most of tbe wat:er in the permeable consolidated formations in the State 1s coniined under artesian pressure by overlying relatively i1lIpermeable beds of clay or shale. The artesian pressure in areas of low elevations are in places great enough to cause wells to flow. Artesian aquifers have substantially cifferent storage characteristics than most of the unconsolidated aquifers. Large amounts of water can be pumped frolll them without dewatering the materials near the well. Pumping reduces the pressure in the aquifer rather than draining water from the deposits as it does in an unconfined aquifer. The pressure surface is a cone- shaped depression centered at the pumping well. The volu!il8 of the cone is a. few to many thousands of times larger than the volume of water pumped and, compared to the volume of the dewatered zone formed in most of the unconsolidated aquifers after pumping the same amount of water, the depressurized zone is a few to many hundreds of times lar~r. Depressur in<J causes the aquifer to compress and the contained water to expand, accounting for the water yielded from the well. Local dewatering in an artesian aquifer occurs only when the pumping level is below the top of the water-bearing zone. Even where the pumping level is low enough to cause dewatering, the zone will fill almost immediately When pumping ceases. 1\t'ter a period of time, which depends largely on the distance of the outcrop from the point of withdrawal, water stored in the outcrop areas will move toward the well. Even though the total amount llIOving toward the well may be large, the rate of lI1OVe.'IleDt in the outcrop areas generally is slow because tl1e area contributing water generally is large. Thus, the water levels in the outcrop areas tend to decline over a large area but at a slow rate. If perennial streams cross the outcrop in the area subject to decline and if they are hydraulically connected with the aquifer, the strean\flow w.ill be reduced. 'l'he loss .in flow will tend to equal ultimately the ground-water-withdrawal rate, although it raay take IllilnY years before the two are nearly equal. In many, perhaps in most, places in Colorado, the reduction in streamflow will be negligible owing to the scarcity of perennial strea."l\S and the lack of extensive areas where they are hydrauli- cally connected with aquifers. As a result, water withdrawn from artesian aquifers generally would ultimately result in a decreasing amount of water in storage in the area of outcrop, but the affected area probably would be small.