American Cordillera
The Turtle Mountains are one of several ranges that constitute the Maria Fold and Thrust Belt. The Maria Fold and Thrust Belt underwent generally thick-skinned (involving basement rocks) North-South trending crustal shortening in the Cretaceous, followed by generally east–west trending large-scale crustal extension in the Miocene. This North-South shortening is anomalous, as crustal shortening in the rest of the North American Cordillera is oriented generally east–west because of the generally east–west compression that was due to the subduction of the Farallon plate under western North America. Also unlike the rest of the North American Cordillera, deformation in the Maria Fold and Thrust Belt involved rocks of the North American Craton, most notably the Grand Canyon sequence of sedimentary rocks.