Well, the San Gorgonio area is a very 'broken' area with many faults. It seems to always have a 'low level hum' going on.

Mammoth lakes being a caldera also has clusters quite regularly.

Lone Pine does have clusters, but not like the above two locations. Further south in the Coso Basin particularly around Coso Junction is well known for regular cluster events.

I'm not too worried about these areas, although they certainly are worth watching. What really gets my attention is when there are clusters where they've not been for a long time, if ever in known history.

In my observation there has seems to be an uptick in activity on faults just north of the Mexican border since the El Mayor quake. The faults involved in that quake are an extension of the Elsinore Fault Zone so I think it's reasonable to be concerned about the rest of the fault, especially since it's capable of upwards to M7.5 quakes. It's recurrence interval is thought to be about 250 years. The last large quake was an M6 in 1910 on the northern end. Is it unreasonable to suspect that that may not have been enough to relieve the stress on the entire length and could be building faster to a large quake due to the change in stress fields after El Mayor? Who knows? Even without that, we should always be aware and be prepared.

I guess the Elsinore Fault Zone gets my attention since I currently reside so close to it.

Brian