Complex sentence: The United States called the reservation the Hoopa Valley Indian Reservation, where the Hupa now reside next to the territory of their neighbors, the Yurok at the connection of the Klamath and Trinity Rivers in northeastern Humboldt County.
Split into simpler sentences: The United States called the reservation the Hoopa Valley Indian Reservation, where the Hupa now reside. The reservation is next to the territory of the Yurok at the connection of the Klamath and Trinity Rivers in northeastern Humboldt County.