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U . S . GEOLOGICAL SURVEY DEPARTMENT OF THE INTERIOR GEOPHYSICAL DELINEATION OF GRANITIC PLUTONS IN NEVADA by

the formation of karst terrain, water percolating underground enlarges subsurface flow paths by dissolving the rock. As some subsurface flow paths are enlarged over time, water movement in the aquifer changes character from one where ground-water flow was initially through small, scattered openings in the rock to one where most flow is concentrated in a few well-developed conduits. As the flow paths continue to enlarge, caves may be formed and the ground-water table may drop below the level of surface streams; surface streams may then begin to lose water to the subsurface. As more of the surface water is diverted undergound, surface streams and stream valleys become a less conspicuous feature of the land surface, and are replaced by closed basins. Funnels or circular depressions called sinkholes often develop at some places in the low points of these closed basins.