Originally Posted by BigDogatPlay
A prohibited area defined elsewhere in statute is anyplace where the discharge of firearms is not authorized. I would take the position solely for the sake of the argument that discharge, other than legitimate self defense, is not permitted off the range itself. As the range is, by the OPs description in a place open to the public, in an unincorporated portion of a county and it can be inferred that recreational discharge would not be authorized where he was at the time, then presumptively the check is within scope.
If he was on a private range, then he was on a private range.
A public place and a place open to the public are two, totally separate things.
Additionally, a police officer may not force you to stop show safe/legal transportation unless you are physically carrying a firearm in public, and they require a warrant to check the contents of your trunk unless under reasonable suspicion or probable cause. Each locked container (think locked pistol case) requires a separate warrant.