Was this a game/hunting violation (so called) or a firearms possession issue? I my area is is not illegal to have a firearm loaded,unloaded, holstered,unholstered, visable or concealed in you vehicle .
Perhaps some vague Game regulation about firearms possession while in proximity to game? Why should you have to prove your innocence on your own property? I am distressed with the "charge them and let the judge sort it out" attitude that seems to prevailing Modus operandi with LEOs these days.