It is proved that the Bottom Aquifer was composed of diluvial alluvial deposition and beds bearing gravel were mainly formed by rapid mud rock flow in fault basins during Miocene epoch when the paleoclimate was warm and dry.

• 各矿区的底含皆形成于气候干暖的新第三纪中新世 ,是一套在中、新生代断陷盆地内的山前洪积扇上由快速水流形成的洪积 -冲积物 ,含砾石地层多为泥石流沉积物