 Several factors led to the Frank Slide . A study conducted by the GSC immediately following the slide concluded that the primary cause was the mountain 's unstable <unk> formation ; a layer of limestone rested on top of softer materials that , after years of erosion , resulted in a top @-@ heavy , steep cliff . <unk> laced the eastern face of the mountain while underground fissures allowed water to flow into the mountain 's core . Local Indigenous peoples of the area , the Blackfoot and <unk> , had oral traditions referring to the peak as " the mountain that moves . " <unk> noticed the mountain had become increasingly unstable in the months preceding the slide ; they felt small <unk> and the superintendent reported a " general <unk> " in the mountain at depths between 1 @,@ 100 metres ( 3 @,@ 600 ft ) and 1 @,@ 500 metres ( 4 @,@ 900 ft ) . They found that coal broke from its seam ; it was said to have practically mined itself . 
