Skeleton Man by Tony Hillerman

Joe Leaphorn, former Navajo tribal police lieutenant, is not a happy retiree. So when his successor asks him to look into how a young Hopi named Billy Tuve came by a valuable diamond the boy tried to pawn for a fraction of its worth, Joe finds himself involved in a five decade old mystery. It dates back to a plane crash in the Grand Canyon, one that took the life of a man whose putative daughter also has an interest in the diamond; it could lead her to her father's remains, from which she hopes to extract enough DNA to establish her birthright. For good measure, Hillerman adds a couple of villains determined to beat her to the site of the crash, a cache of other diamonds long since given up for lost in the Canyon's watery depths, and a Hopi ritual that's kept the site secret for years. It's a good yarn, well but twice told; Hillerman sets it up in a chronologically confusing opening chapter, in which Joe spins the story for a couple of former law-enforcement colleagues--not just to entertain or enlighten them but to demonstrate what he calls his "Navajo belief in universal connections. The cause leads to inevitable effect. The entire cosmos being an infinitely complicated machine all working together."