Waterlily (Ella Cara Deloria, c 1988 but written several decades earlier) is a work of ethnography in the guise of historical fiction, exploring the customs of the Dakota people through the childhood and coming-of-age of a 19th century girl. (I'm not sure of the date, but it's at some point where there were American forts and trading outposts on the plains, but before homesteading. 1840's, maybe?)
By ordinary novel standards, the plot is meandering and slight, and there's way too much tell and too little show. But as a glimpse into a bygone world and its customs, it works very well.