Wow Don! Something's going on there for sure.

I don't think what you are seeing is magnetic though - its ELF - well maybe it is associated with magnetics after all. Here is from the site:
ELF stands for Extremely Low Frequency. But what does that mean and how does it correlate to earthquake tracking? Magnetic field fluctuations are created prior to an earthquake. Only the extremely low frequency portion of this signal survives the transfer through the surrounding earth. No one knows for sure what causes the field fluctuations, but many researches have observed the signals.

Those readings have been whacky all month - and lesser odd readings back into april - I wonder if the instruments are working properly? Aren't there some quarrys near there?

On another note - Long Beach City College Geology Club is taking on the project of assembling one of these monitoring sites and collecting data! I'm Excited!

Canie