If there was an explosion you can be pretty sure it was a meth lab and not a pot growing operation. There is a reason nobody picked up the house after 6 months - you will need a contractor that is licensed to clean this up. It will be tough to estimate the cost before buying the structure. Here the information and regulations for CA. Needless to say, CA is one of the states that takes hazardous waste and exposure to hazardous chemicals very seriously.
Methamphetamine Drug Lab Cleanup Program
You can't even buy this assuming it is worth only the lot. Your cost to dispose of the waste and the possibility of having to excavate soil make even that tough to calculate ...
I guess it would really take an expert to buy this. Someone that is a certified cleanup contractor, has access to the testing for contamination levels, can test before buying and has a clear idea what disposal of the contaminated materials will cost.
I have read that some of these houses are burnt down in controlled burns. Not sure if that's legal in CA.
G