Idaho Statute 18-3302
(7) Except in the person's place of abode or fixed place of business, or on property in which the person has any ownership or leasehold interest, a person shall not carry a concealed weapon without a license to carry a concealed weapon. For the purposes of this section, a concealed weapon means any dirk, dirk knife, bowie knife, dagger, pistol, revolver or any other deadly or dangerous weapon. The provisions of this section shall not apply to any lawfully possessed shotgun or rifle.
(12) The requirement to secure a license to carry a concealed weapon under this section shall not apply to the following persons:
(d) Any person outside the limits of or confines of any city while engaged in lawful hunting, fishing, trapping or other lawful outdoor activity;
INAL but I would say that according to 12(b) you would be okay since it is on private property, it is an outdoor ranch, not located in a city and you would be participating in a "lawful" outdoor activity. Ie, tending the ranch, or just out there goofing off you would still need to protect yourself from hostile wildlife or intruders on the ranch.
Maybe someone with more ID experience will chime in.
http://legislature.idaho.gov/idstat/Title18/T18CH33.htm Link to ID statutes