距今2．4亿年前后的二叠纪,贺兰山豁开了一条东西走向的大口子,它婉蜒30公里,直抵贺兰山最高峰砂锅洲。这条平均宽度不足50米的沟谷,就是贺兰山岩画的荟萃之地一贺兰口。从沟口延伸560米的两侧山崖和伸向谷底的坡石上,分布着708个大小不等、形象怪异的人面像。其中有8处崖壁卧石面上,平均每平方米竟磨 The Permian dating back to 240 million years ago, Helan Mountain excavated an east-west big mouth, which stretches for 30 kilometers and reaches the Helan Mountain peak casserole. This average width of less than 50 meters of the valley, Helan Mountain Rock paintings is a meta-Helan mouth. Stretching 560 meters from Mizoguchi on both sides of the cliff and toward the bottom of the slope stone, the distribution of 708 different sizes, the image weird face. There are 8 cliffs on the stone surface, the average actually grind each square meter