Why have a large number of bamboo slips been unearthed in Gujuyan area?

The ancient Juyanhai was a garrison place during the Han and Jin Dynasties, and a large number of bamboo slips written at that time were completely preserved because of the dry local weather. What is particularly valuable is that many bamboo slips are written with specific dates, such as four years in Yong Guang and five years in Yangshuo. These bamboo slips left first-hand information for people to understand the calligraphy level and style at that time.