The Collaborative International Dictionary of English v.0.48:

Klamaths \Kla"maths\, prop. n. pl.; sing. Klamath (Ethnol.)
   A collective name for the Indians of several tribes formerly
   living along the Klamath river, in California and Oregon, but
   now restricted to a reservation at Klamath Lake; -- called
   also Clamets and Hamati.
   [1913 Webster]