http://www.amazon.com/Heart-Chief-Joseph-Bruchac/dp/014131236X
Reading The Heart of a Chief will most definitely help your understanding of the book. It is very similar to High Elk's Treasure, in the way it has a Native American protagonist. He lives on a reservation in present-day America. He is a teenage boy who cares about his background, just like Joe. There are actually many similarities between Chris, the main character in The Heart of a Chief and Joe. This novel may actually spark an interest in Native American culture, leading you to read High Elk's Treasure. This novel will also add to your understanding of hardships Native Americans have gone through.
My personal reaction to The Heart of a Chief was that is told in a very fiction way, but it has a lot of true, common events, such as the casino being built on the reservation's land. There are casinos on many Indian reservations. I also thought that it was incredibly similar to High Elk's Treasure. It is about a regular teenage boy living his life, going to school, and trying to preserve a historical home. Also, this is a book by Joseph Bruchac, who is a great author.