Do you have to have the "physical" contract to file a preliminary notice. Isn't once "Intent" is established or a Notice to Proceed?
Yes, a contractor can send a preliminary notice even if there's not a written contract signed. For one, CA peliminary notices can be sent early. For another, preliminary notices are really just informational letters, so anyone can send the notice (granted, whether lien rights exist is a different story). And, finally, note that CA doesn't require a written contract in order for lien rights to exist.
If you have other questions about CA preliminary notices, or if you just want to learn more, this page will be useful: California Preliminary Notice Rules & FAQs.