Using something more sophisticitated than a ruler geologists are now able to see a better pattern in the earthquake activity.
Scientists now estimate that earthquakes occurred on that section of the fault in 1417, 1462, 1565, 1614 and 1713.
With the last one over 15o years ago and with an average occurance of 88 years it is time.
This has all been determined by diggings in the Carrizo Plain that is north of LA in San Luis Obispo county where the San Andreas fault is a prominent feature.
Study shakes up scientists’ view of San Andreas earthquake risk – Los Angeles Times.