Turtle Mountain stand immediately south of Frank . It consist of an older limestone layer folded over on top of softer materials such as shale and sandstone . Erosion had left the mountain with a steep overhang of its limestone layer . It have long been unstable ; the Blackfoot and Kutenai peoples called it " the mountain that move " and refused to camp in its vicinity . In the weeks leading up to the disaster , miners occasionally felt rumblings from within the mountain , while the pressure created by the shifting rock sometimes caused the timbers supporting the mine shafts to crack and splinter .