So they acquired rock samples from boreholes drilled through the presumed Sevier Desert fault in 1980 and 1982 by the Atlantic Richfield Oil and Gas Co. Subjected to tremendous shearing as they slide against other rocks, brittle rocks just above a fault usually fracture, but the Lamont-Doherty scientists found no evidence of the expected microfractures within rocks in the Sevier Desert specimens. Furthermore, rocks beneath the surface, which according to the fault interpretation were originally deeper and therefore closer to the earth's hot interior, should show evidence of being stretched like taffy as crustal blocks slid against one another. The scientists found no evidence of this, either. Anders and Christie-Blick also offered an alternative explanation for the steep faults intersecting the presumed Sevier fault. Sediments in the area are full of salt, and recent oil companies' boreholes have cut through salt deposits nearly a mile thick.
Salt is less dense than rock and tends to mushroom upward forming salt domes.
As salt migrates up, adjacent sediments collapse downward to fill spaces the salt vacated. That indicates that salt migration may have sparked the faults' creation, not large-scale regional extension of the earth's crust, as had been believed, the scientists said. More evidence was provided by Lamont-Doherty paleobotanist Kathryn Gregory. Assuming the top wedge did slide some 23 miles along the fault over the past 26 million years, as other scientists have said, geologists can mentally slide the wedge upward and eastward to reconstruct the wedge's original position. The research has been supported by the National Science Foundation.