Tse is Navajo for rock. It's pronounced sort of like the "ts" in "tsunami". Not a pure "s", but one with the t preceding it. Kinda like the sound between the words "hot seat", where your're picking up both the T and the S. Sorta. See if this helps:
Navajo Pronunciation Guide
There's also a book about Navajo place names that Hillerman wrote I think. Or maybe it's someone else's and it's about the places in his books. Anyway, it's a good reference if you want to know more.