Here is the motion in Confederated Chehalis Tribes v. Thurston County Board of Equalization:
The federal regs are here. 25 CFR 162.017 reads:
Subject only to applicable Federal law, permanent improvements on the leased land, without regard to ownership of those improvements, are not subject to any fee, tax, assessment, levy or other charge imposed by any State or political subdivision of a State. Improvements may be subject to taxation by the Indian tribe with jurisdiction.