State Law
Machoduck, a direct lift from your post: "State laws regarding the concealed carry of firearms and the carrying of weapons within or on a motor vehicle apply to all National Forest System lands." The answer you get is not found in Federal law or regulation, but in Virginia Administrative Code. As follows.
4VAC15-40-60. Hunting with dogs or possession of weapons in certain locations during closed season.
A. ... national forest lands statewide. It shall be unlawful to have in possession a bow, crossbow, or any firearm that is not unloaded and cased or dismantled on all national forest lands statewide and on department-owned lands and on other lands managed by the department under cooperative agreement located in counties west of the Blue Ridge Mountains except during the period when it is lawful to take bear, deer, grouse, pheasant, quail, rabbit, raccoon, squirrel, turkey, or waterfowl on these lands.
D. Shooting ranges and authorized activities. The provisions of this section shall not prohibit the conduct of any activities authorized by the board or the establishment and operation of archery and shooting ranges on the lands described in subsections A, B and C of this section. The use of firearms, crossbows, and bows in such ranges during the closed season period will be restricted to the area within the established range boundaries. Such weapons shall be required to be unloaded and cased or dismantled in all areas other than the range boundaries. The use of firearms, crossbows, or bows during the closed hunting period in such ranges shall be restricted to target shooting only and no birds or animals shall be molested.
F. It shall be unlawful to possess or transport any loaded firearm, or loaded crossbow in or on any vehicle at any time on national forest lands or department-owned lands.
G. The provisions of this section shall not prohibit the possession, transport and use of loaded firearms by employees of the Department of Game and Inland Fisheries while engaged in the performance of their authorized and official duties, nor shall it prohibit possession and transport of loaded concealed handguns where the individual possesses a concealed handgun permit as defined in § 18.2-308 of the Code of Virginia.
For the purpose of this section, the word "possession" shall include, but not be limited to, having any bow, crossbow, or firearm in or on one's person, vehicle or conveyance. For the purpose of this section, a "loaded firearm" shall be defined as a firearm in which ammunition is chambered or loaded in the magazine or clip when such magazine or clip is engaged or partially engaged in a firearm. The definition of a loaded muzzleloading firearm will include a muzzleloading firearm that is capped, or has a charged pan, or has a primer or battery installed in the firearm. The definition of a "loaded crossbow" is a crossbow that is cocked and has either a bolt or arrow engaged or partially engaged on the shooting rail or track of the crossbow, or with a "trackless crossbow" when the crossbow is cocked and a bolt or arrow is nocked.
Unless you have a permit, you cannot cross National Forest Land to get to the Trail with a loaded handgun. I suppose you could unload and case the firearm until on the trail.