The Blue Beneath the Mountain by John Opalenik
Riley and her best friend Matt are going their separate ways. Before they do, they intend to travel together. Not to anywhere special. To them, it’s not where you’re traveling, but who you’re traveling with that makes it special. Soon they arrive in the small town of Altum, an oasis in the desert hiding a terrible secret. A secret that has been living inside the mountain far longer than even the citizens of Altum know. What dwells within the mountain will change their lives and their friendship forever.