The peak is composed of banded biotite tonalite of fine mediate grain developing in Mengshan rock suit of Fuping period 由27亿年左右形成的太古代阜平期蒙山岩套条带状中细粒黑云母英云闪长岩构成，柱状节理发育，差异性风化剥蚀作用强烈，组成云蒙“山”峰，俗称“挂心崛子”，形容云蒙峰之陡峻。