The Mexia fault zone is a series of overlapping faults, all trending in a direction a little oblique to the trend of the zone as a whole. All have a downthrow on the west, or on the side up the regional dip of the strata. This series of faults passes through Milam, Falls, Limestone, Freestone, Navarro, Henderson, and Kaufman counties. In Limestone, Freestone, and Navarro counties eight oil and gas pools have been discovered associated with major faults in this zone. From the south northward these are the South Groesbeck, North Groesbeck, Mexia, Wortham, Currie, North Currie, Richland, and Powell fields. Three or four miles west of the Mexia fault zone is another parallel series of faults, the Tehuacana zone, in which there are now two oil fields (Nigger Creek and Cedar Cr ek).

All these ten fields yield their principal production from the Woodbine sand. Up to December 31, 1927, 212,544,366 barrels had been produced from the ten pools, or about 28,300 barrels per acre.

Evidence points to the conclusion (1) that the faulting occurred partly in post-Cretaceous, pre-Midway time and partly in post-Wilcox time; (2) that the oil had its source in the Eagle Ford shale or in shales in the Woodbine formation, or in both; (3) that it came into its present reservoirs after faulting; and (4) that it reached its present position by lateral migration rather than by migration up the faults from a deep source.