Yes, POTLATCHES is a Scrabble word!

Letter values in Scrabble US: P 3, O 1, T 1, L 1, A 1, T 1, C 3, H 4, E 1, S 1.

Is it a valid word?

POTLATCHES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a ceremonial feast held by some Indians of the northwestern coast of North America (as in celebrating a marriage or a new accession) in which the host gives gifts to tribesmen and others to display his superior wealth (sometimes, formerly, to his own impoverishment)