This is a scanned copy of a letter written by Spokane Garry from the Red River school in Winnipeg, Manitoba. This document confirms that Garry’s tribal name was Slough-Keetcha.
You can download the GarryLetter.
Three Salish words appear in Garry’s letter: Illemechum, Chungulloosun, u Slough-Keetcha. It seems clear that Illemechum refers to the Salish word for chief, ilmixʷm. Chungulloosun and Slough-Keetcha are personal names, but their meaning is unclear. One possible transcription of Garry’s Salish name is sloʕ’ʷq’ʔič.