@Emily1452
We are also in California and in an unincorporated area. Our county has a bunch of requirements and an ordinance that governs our short term home share business. If you received a letter, they are aware of your business, and expect you to come into compliance. Most counties and cities are using a tracking software that easily finds all of us. The best information would be to pay a visit to the county planning and zoning office. They will provide an outline of what you need to do to to become legal.
If you were in my county, you would be considered a short term rental, and definitely be required to register, comply with their requirements, collect and remit TOT, and agree to comply with the local ordinance governing STR. Some of the items on the list include agency inspections around fire prevention, emergency access/egress plus other public safety issues, parking, noise, impacts on neighbors, number of guests, infrastructure and business insurance coverage.
Let us know what happens!