The Davis sand lens of the Hardin field is in the Eponides yeguaensis zone of the Yegua (upper Eocene) formation.

The sand was first recognized as a separate sand in the Woodley Petroleum Company's Emma Davis well No. 1 where it was encountered from 7,511 to 7,525 feet below the surface. Two gas and distillate wells and one oil well are now producing from the sand. The bar is a separate and sealed reservoir.

An isopach map of the interval containing the Davis lens shows a marked thickening within the area where the best development of the Davis sand is found. It discloses that the bar has a long axis of approximately 11,000 feet, an average width of approximately 1,250 feet and a total area of practically 320 acres. The contours of the isopach map are lines of sedimentation from which the section to be penetrated may be postulated in advance of the drill.

The Davis "zone," wherein the lens is found, is composed of alternating sand, sandy shale, and shale and is arenaceous in character, indicating lagoonal or tidal-flat deposition. The Davis sand is composed of 98 per cent quartz; it is medium-grained in texture, whereas the typical Yegua sands are fine-grained.

The Davis lens was laid down as a barrier beach or off-shore bar by a retreating Yegua sea.