In the Canon:-=== One-Man-Bucket, Mrs Cake's spirit guide, and his twin brother Two-dogs, originated from a Red Indian tribe on the Central Howondaland Plain.
From clues in context it might have been this one:-
In the Pessimal Discworld:-Edit
The Latoka Sioux are possibly the most numerous and powerful tribe among the Central Howondalandian Red Indians. Led by their dour and unsmiling chief, er, Squatting Bull, they bring together as many of the other tribes as they can to fight an invasion from White Howondaland.
the Latoka - the word means, to other Indians, they who smoke much of the Holy Herb - are a Plains tribe, who ride fast strong ponies and live in tepees. Their principal god is Coyote, and they revere the Living Wood.