This work address two fundamental, yet unanswered, questions about the southern San Andreas Fault (SSAF) in California:  (1) Why has the SSAF not produced a large earthquake rupture in ~300 years, even though the average recurrence for the last five earthquakes is ~180 years; and (2) What mechanism can explain the twenty years of research that show an apparent correlation between high-stands of Lake Cahuilla and large earthquake ruptures on the SSAF.  We propose that prehistoric flooding of Lake Cahuilla (which encompassed an area significantly larger than the present day Salton Sea) may have been a catalyst in triggering a sequence of large earthquakes in Southern California in the past. One of the most plausible sequences is that stresses generated by the lake-load promote rupture on faults beneath the lake, and these in turn promote rupture on the SSAF.  Geological observations and theoretical stress models suggest that the role of both the lake level and rupture of faults beneath the lake are an important component in this triggering sequence. This suggests that a large rupture on the SSAF has likely been delayed because of the absence of extensive Lake-loading within the last 300 years.

Plate tectonic boundary (red line) between the North American Plate (upper right) and Pacific Plate (lower left).  Black arrows represent plate tectonic motion.