Hi Tony, yes, I noticed that quake as rare for the last decade or 2 that I have been watching, but I missed that it was on the anniversary.

The maps show it 1 or 2 km west of San Andreas lake along highway 880(?). The main fault, I think, is in the lake. But, if the main fault is not dead vertical, and dips steeply to the SW, could be on the main fault. The main fault may be a zone with width. However, in Carrizo and some other places the stream offsets show that at the surface the quakes break the same strand repeatedly.

The focal mechanism is consistent with right-lateral on a NW-SE fault. Might not be a terrible idea to monitor this area for the kind of tremor that years later they saw was in the lower crust before the 2004 Parkfield quake. Bring in more instruments (although there are presumably a lot of instruments already).
Chris