In 1865, S.H. Greene recorded a map depicting a subdivision of Greene’s property into lots. There was no applicable subdivision-map regulation in 1865. Consequently, Greene’s map was recorded in Sonoma County (Sonoma) (defendant) without review by any public entity. In 1893, California enacted the first statewide subdivision-map statute, authorizing the approval of subdivisions by local agencies. Subsequently, California passed the Subdivision Map Act (SMA). The SMA vested the authority to regulate subdivisions in local governments and prohibited the sale, leasing, or financing of any parcel of a subdivision until the subdivision was recorded on a lawfully approved map. However, the SMA created an exception under California Government Code § 66499.30 for any parcel offered for sale or lease in compliance with subdivision laws that were in effect when the subdivision was established. The SMA also included § 66451.10(a), which prevented localities from automatically merging contiguous parcels previously created under or exempted from the provisions of the SMA or any prior applicable law. In 1996, Jack and Jocelyn Gardner (plaintiffs) possessed 158 acres of Greene’s former property (the property). The Gardners applied to Sonoma’s permit department, seeking recognition that the property consisted of 12 parcels that could be sold, leased, or financed separately under the SMA. The permit department denied the Gardners’ application, because Greene’s map had been recorded before 1893 and thus had not created cognizable parcels. The Gardners appealed to Sonoma’s planning commission, which denied the appeal and recognized the property as a single parcel. The Gardners appealed to the County Board of Supervisors (the Board). Because the property had been conveyed as a single unit since 1865 and the 12 lots had never been conveyed separately, the Board denied the Gardners’ appeal. The Gardners filed a petition in superior court for a writ of mandate, which was denied. The court of appeal affirmed the denial, holding that the SMA’s legislative intent precluded the recognition of subdivision lots recorded before 1893. The Gardners appealed, arguing that § 66499.30 and § 66451.10(a) compelled the recognition of the 12 parcels.