A Tale of Two Sands

By Henry Walrond, consultanting Geologist, Bakersfield, CA

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ABSTRACT

This report is on the relationship of, and possible source connection between, two of the largest Eocene sand bodies in the southern San Joaquin Basin, the Lower Eocene Cantua/Gatchell/Yokut series of the Coalinga Area and the Upper Eocene Point of Rocks that extends south along the west side of the basin from Pyramid Hills to Elk Hills. It seems to be more than coincidence that the Point of Rocks deposition would start almost immediately after the deposition of the Lower Eocene sands stopped in the Coalinga area. This curious sequence or apparent transfer of sand deposition from one area to the other (north to south, pre-Domengine to post-Domengine) without overlap of deposition in time suggests a genetic connection.

The study ties most of the Lower and all of the Upper Eocene sands to a common westerly marine basin (La Honda), and source terrain (Gabilan granites). Included is an explanation for the pre-Domengine salt section reportedly penetrated by a well at Elk Hills. Also included is a scenario for the dramatic and widespread Domengine transgression that rapidly covered the southern San Joaquin basin initiating in the Upper Eocene, and how this relates to the unusual juxtaposition of the shallow water transgressive Domengine sand and the immediately overlying bathyal Kreyenhagen shale.