I know that a Class A roof is a well proven option in wildfires, but I understand sidings such as vinyl, and chemically treated wood are permitted under the CA wildfire code. I am concerned that vinyl siding is not ideal in wildfire zones and question whether the chemical treatment on wood will maintain its performance over the years after weathering and exposure to the sun and elements. Are there suggested best practices for siding materials?

Yes, there are a number:

• Cement Siding – this is viable option and good defense against ignition.  However, fire tests show and post wildfire events show that burn-through even cement sidings can happen, allowing flame to enter the wall cavity.  Certain profiles such as ship lap, with long running lengths of gaps, small panels the resemble shakes, and even large panels where gaps may be covered by cement battens are all susceptible to flame penetration into the wall cavity.  A best practice is to ensure that there is a non-combustible backer such as Type X fire rated gypsum board or mineral wool board insulation of at least 1″ thickness behind cement siding.
• Vinyl, Chemically Treated Wood, and Combustible Sidings – if these sidings are to be used or permitted, as with the cement siding, these should have a backer of Type X gypsum or mineral wool to protect the wood structural sheathing and block entry of flame into the wall cavity.
• Meeting the Energy & Wildfire Codes: It should be noted that where mineral wool board is selected, this can help with meeting the CA energy code as well as fire hardening objectives.
• Concrete Sandwich Panel Construction: while wood frame construction is the predominant construction method in North America, one practice that would be a suitable option in wildfire areas would be a sandwich panel comprised of a concrete outer shell with a core of rigid foam insulation.  Such types of construction are generally more expensive than traditional wood frame but that can be attributable to it’s uncommon.