Tree ring cores of spruce (Picea crassifolia) were taken from Helan Mt, which is the boundary of the monsoon areas and westerly, and also the margin of the arid and semi-arid China with a climate that is transitional between temperate monsoon and continental and mountain, were used to construct a 93 year width chronology. All statistic characters indicate the chronology is stable and must record some certain environmental factors. It should be one of the important proxies to study this sensitive region of m...