Leveling by the United States Coast and Geodetic Survey in 1951 showed a general land-surface subsidence in the Houston-Galveston region, Texas, since previous leveling in 1943. The region of subsidence coincides with a region of large-scale ground-water withdrawals where the water is pumped from a series of unconsolidated sands interbedded with clay layers. In the northern part of the region the ratio of land-surface subsidence to decline in artesian pressure head is about 1 to 100. In the southern part of the region, where there is a greater percentage of clay in the section, the ratio is greater. The subsidence is attributed to compaction of the clays as the artesian pressure in the sands is reduced. From a comparison of the volume of subsidence to the volume of water pumped, it appears that about one-sixth of the water pumped has been supplied from storage in the clays.

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