Mappa topografica Big Spring

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Big Spring

The spring was sourced from a relatively small aquifer situated on the northern end of the Edwards Plateau and the southern end of the High Plains, being, structurally, a collecting sink of lower Cretaceous (Fredericksburg) limestones and sands. The spring aquifer held a large quantity of water due to the great number of fractures, solution channels, and interstices in the rocks and underlying sands, although the areal extent of the Big Spring sink is estimated to be only 1 mi (2 km) in diameter, with the main area only 3,000 ft (914 m) wide and almost circular, with some ellipticity trending towards the west. The Cretaceous beds subsided about 280 ft (85 m) below their normal position, centered on the southeast quarter of Section 12, Block 33 T1S; T&P RR Co survey, and the entire stratum appears to be preserved within the sink, the surface topography roughly following the subsurface subsidence. This writing identifies the sink as one of a number of similar subsurface geologic features in the surrounding area, differing from the Big Spring sink only in the fact that the surface topography above the others, while showing some decline, does not dip low enough to intersect the top of the water tables; hence, no springs could form from the other aquifers. In a passing comment, enigmatic in its content and disappointing in its brevity, the report states no other comparable deep sinks formed elsewhere on the Edwards Plateau.

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