The first place to look is your construction contract. Under California law, remodeling or "home improvement" contracts require specific disclosures and other provisions. One of the items to look for is a provision concerning the contractor's agreement to comply with building codes and other applicable laws and regulations. That may establish the basis for a breach of contract claim.
If the contractor did not finish his scope of work, then you may have a claim against the contractor's license bond, and a basis to file a complaint with the Contractors' State Licensing Bond. If the contractor had employees, but he did not carry worker's compensation insurance, then he may not be considered a licensed contractor, and may be obliged to return the entirety of all compensation received from you on this project.
Consultation with an experienced construction attorney certainly makes sense in this situation.
First, the contractor does not need any authority from the trust. You have the right to posses he property, and therefore, you have the right to have a contractor do work on the property. As a renter it is your duty to return the property in the same condition you received it, but that does create any duty on the part of the contractor.
With that said, you can sue the contractor for your damages. In this case your damages would be the cost to hire someone else to finish the job. You should consult an attorney to determine the likelihood of success based on your contact and the work completed.
I hate to say it, but shame on you for paying the contractor before he was done. Now that that's out of the way, as a consumer in a construction contract in California, you have many rights and remedies. The Home Improvement Act (Business & Professions Code section 7150.1 to 7167) applies to this contract and it sounds like the contracvtor has violated many provisions of it. As a result, you can get some assistance from the Contractors State License Board by filing a complaint. Go to www.cslb.ca.gov. Also, you can file a claim up to $12,500 on the contractor's license bond. Information on who his bonding company is and their contact information can also be found on the CSLB's website. By using the CSLB and the bonding company to keep the pressure on, you'll probably get this guy back to finish the job or get the necessary funds from the bonding company. It's a rigorous process but it works if you keep at it. God luck!
Attention: This response is based upon general legal theories and may or may not specifically address issues that affect your individual legal matter or situation. It should not be relied upon outside of the jurisdiction(s) in which the attorney is licensed to practice as each state has different laws. Each situation is fact specific and requires comprehensive legal evaluation following a thorough consultation and review of all the facts and evidence available. This response does not create an attorney-client relationship between the asking and answering parties.