Situated in the southwest, bounded by mountains and watered by the Yangzi and several tributaries, the region occupied by the former Warring States-period state of Shu was secure and rich in both agricultural and mineral resources. An abundant supply of copper and tin had led to the rise of a bronze-producing society at Sanxingdui, contemporary with the Shang at Anyang (c.1200 bce), and later, salt, iron, and natural-gas deposits were developed into thriving industries during the late Zhou period. Moreover, quality soil, easy access to water, and a warm and lengthy growing season made the region highly productive in terms of agriculture. After Shu was conquered by Qin in the third century bce, a large number of families from the Central Plains were relocated to the area to provide material support for the Qin war effort. It was due in no small measure to the resources extracted from Shu that Qin was able to conquer and unify China by 221 bce.