Normally I'd agree that it's a sensor on the fritz. But what becomes clear, looking at the 30 day charts (instead of the 7 day charts),is the following:

Presidio-N is continuing its downward trend, as is Presidio-E (in spite of chaotic readings).

Beginning 6/9,Berkeley-N began to climb (maybe damaged in 2.6 E. bay EQ-plausable).

Beginning 6/19, Berkeley-E began its climb (4 days after Gilroy quakes).

So, either 4 separate instruments, in 2 different locations, on opposite sides of the bay are going haywire, or???
If anyone has any ideas, please post them.
Thanks.

Logged EQ's in general area:
6/6/06,2.8,Clearlake(NNW of SF), http://neic.usgs.gov/neis/bulletin/neic_nqbx.html

6/7/06,3.3,Ukiah (NNW of SF), http://neic.usgs.gov/neis/bulletin/neic_nqcc.html

6/7/06,3.0,Soledad (SSE of SF), http://neic.usgs.gov/neis/bulletin/neic_nra7.html

6/9/06,2.6, East Bay, http://neic.usgs.gov/neis/bulletin/neic_ntci.html

6/15/06,4.3,Gilroy (SSW of SF), http://neic.usgs.gov/neis/bulletin/neic_nzar.html

6/15/06, 3.0, Gilroy (SSW of SF), http://neic.usgs.gov/neis/bulletin/neic_nzcv.html