Tunnels & "Caves" in Napa Valley, California?
Under Speaker Pelosi's vineyard possibly?
-Building permits.
-Changes in county tax assessment.
In some counties the tax assessor documents change in the assessment photographically.
The person seeking a building permit generally has to submit plans and diagrams for approval.
These can be found in the county tax records.
Some counties let you search tax and property records for free.
Some provide access to permit-related documents online.
Avenues for digging?