Ancient Nitrate Refining Site at Danxia Cave

　　This site is situated in Xiaotun Village, Yuezhao Township, Zhongshan District, Liupanshui City, within the provincial scenic area of the A’er River. It was established during the Kangxi era of the Qing Dynasty. The cave entrance faces a major river (the main upstream branch of the Wu River) and stands about 150 meters above the water level. The cavern is a massive chamber, extending over 900 meters in length, with an average width of approximately 100 meters and an average height of around 60 meters.

　　The western entrance serves as the access point, measuring about 150 meters in width and 50 meters in height. The eastern exit is roughly 100 meters wide and 30 meters high. Inside the cave, the space is spacious and well-lit, scattered with dozens of piles of mining slag. Preliminary estimates suggest the total volume of slag accumulation is around 2 million cubic meters. Among the slag heaps, 23 nitrate boiling stoves, 20 sedimentation pits, 2 water storage pools (with water), and 2 water diversion facilities connected to the cave ceiling remain irregularly. On a massive, bun-shaped calcium deposit measuring 12 meters in length, 4 meters in width, and 2 meters in height, a catchment pool was manually carved. On both sides of the pool, two narrow water guide channels—each 5 centimeters wide and 3 centimeters deep—were chiseled to direct water directly into an adjacent man-made pool. Other pools were built directly beneath dripping points on the cave ceiling.

　　Based on the number of surviving nitrate boiling stoves and water storage pools, it is estimated that this refining site produced around 600 jin (approximately 300 kilograms) of nitrate per day. Judging from the slag accumulation and comprehensive survey data, at least around 300 people were working here daily, indicating that this was a large-scale nitrate production facility. Whether such large-scale extraction was for military or civilian use remains a subject for further in-depth research. The cessation of mining likely occurred during the Yongzheng era or even later. Given the enormous volume of slag accumulation, and based on currently available information, this site is believed to be the largest single-cave nitrate refining site in China.