At present North Dakota does not allow carrying of weapons in "publicly owned parks where hunting is not allowed by proclamation", but hopefully the new bill to remove public gathering restrictions will fix that.
ETA: How long will this last in the Obama administration? Is it solid for a while?
ETA2: Looks like it doesn't matter if state law allows carry in parks, you are still good to go in National Parks if you can carry in the state they are in. More analysis will be needed on this.