A more thorough explanation:

The McClanahan presumption is a legal principle that assumes that states do not have the authority to tax Native American tribe members who live or work on tribal land. This presumption is not limited to formal reservations but also includes informal reservations, dependent tribal communities, and tribal allotments.

For example, if a member of a Native American tribe lives on tribal land and earns income from working on that land, the state cannot tax that income. This is because the McClanahan presumption assumes that the state does not have jurisdiction over tribal land and its inhabitants.

The McClanahan presumption was established in the case of McClanahan v. Arizona Tax Comm'n, where the Supreme Court ruled that states cannot tax Native American tribe members who live or work on tribal land without clear congressional authorization.