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The DOSECC Cajon Pass well is located 4 km NE of the San Andreas fault in a region that includes a diversity of secondary structures. Active faults close to the well are subparallel to the right-lateral San Andreas fault but exhibit left-lateral and normal slip. The stress orientation measured in the well is not consistent with right-lateral slip on the San Andreas fault or the stresses inferred from focal mechanisms of earthquakes within 10 km of the fault, but may drive the E-striking, slightly normal, left-lateral Cleghorn fault, the closest active fault to the well. If the in-situ stress is everywhere consistent with the highly variable styles of active secondary faulting like the Cleghorn, the orientation of stresses along the San Andreas fault may be quite variable.

Borehole breakouts are caused by unequal stress concentrations around a borehole resulting in shear failure of the borehole wall and creating hole elongation perpendicular to the maximum horizontal in situ stress. Breakouts in Tertiary sedimentary rocks were identified in 10 holes in the West Coalinga, Cantua Creek, and West Haven oil fields in the western San Joaquin Valley. The deeper and more reliable (1.5 to 3.7 km) breakouts were oriented northwest, indicating northeast compressive stress, perpendicular to the major fold axes in the San Joaquin Valley and at a 70°–90° angle to the major strike-slip faults in the Coast Ranges. This stress direction is consistent with a reverse slip component on northwest-trending faults in the region and with the focal mechanisms reported for the May 1983 Coalinga earthquake. The existing literature on stress measurements in central and southern California indicates that on a regional scale, the stress regime is transitional between thrust and strike-slip faulting. A hydraulic fracture test in the Kettleman Hills oil field at 3 km depth indicates that this stress regime exists in the upper crust near Coalinga as well.