CA firearms laws do not apply on their land.They are their own nation.
True.
However, CA law is recognized on reservations that contract with the county sheriff to provide law enforcement support.
Such as, the Mission Band of Morongo Indians. Which has a contract with the Riverside County Sheriff Department (RSO) to provide law enforcement support on their reservation.
The Morongo Reservation Patrol frowns heavily on non-tribal members being on the reservation. If you are on the reservation and not an invited guest of a tribal member, tribal employee or tribal member you will be approached and be escorted off the reservation. If you are armed with any type of weapon, you will be detained and RSO will be contacted. If the tribal members catch you on the reservation, depending on who they are, chances are they will assault you and dump your body (This has happened numerous times. Most famous tribal member killed a US Marshall and several tribal members are currently in state prison for shooting at LEOs that went on the "rez" without permission).
The Morongo Tribal Security Department enforces the "no weapons" allowed on Morongo Casino Resort Spa and Casino Morongo property. Guests carrying knives/pepper spray are typical informed to secure such items in their vehicles.
DO NOT carry a firearm inside casino property, unless you are a LEO, you will automatically be marked as a armed robbery suspect and RSO will be contacted.
If you abide by CA firearm transport law, there should be no reason why either the Morongo Tribal Security Department and/or the Morongo Reservation Patrol should know you have a firearm(s) in your vehicle.
The Morongo Tribal Security Department does allow guests to have firearms in their vehicles as long as they are unloaded and secured in locked containers. However, they will not allow you to bring any firearms, even unloaded & in locked containers, into the casinos and hotel.
(Outside okay, inside not okay.)
The Executive Director of the Morongo Gaming Agency is anti-gun. Has similar views on gun ownership as LASO Chief Lee Baca.