Firearms/OC in NM state parks

OK? or no.

No guns allowed in state parks outside of your vehicle.

Nope, except...

19.5.2.20 FIREARMS AND BOWS: Visitors shall not possess firearms, including concealed firearms, with a cartridge in any portion of the mechanism or discharge firearms, including concealed firearms, arrows and air or gas fired projectiles, weapons and other devices capable of causing injury to persons or animals or damage or destruction of property in the state parks system, except during designated hunting seasons or in authorized areas. No such activity is allowed within 300 yards of a developed park area or occupied campsite. 19.5.2.20 NMAC does not apply to on duty law enforcement officials.
[19.5.2.20 NMAC - Rp, 19.5.2.20 NMAC, 1/1/2008]

Must be unloaded

"Visitors shall not possess firearms, including concealed firearms, with a cartridge in any portion of the mechanism..."

Sounds pretty cut and dry to me. You can have one, just no bullets in any part of the gun. I've heard of people open carrying California style (No cartridges in the gun, mags on belt) in NM State Parks and have no trouble with rangers except that they want to make sure you're unloaded.

Also remember that it's legal to carry concealed in New Mexico without a permit as long as the gun is unloaded, so you can concealed carry in the state parks just the same with or without permit.