What is the origin of Naiheqiao and Mengpo Tang?

At the end of the road, there is a river called Forgetting River and a bridge called Naihe Bridge. Walking across Naihe Bridge, there is an earthen terrace called Wangxiang Terrace, and there is a pavilion next to Wangxiang Terrace called Meng Po Pavilion. A woman named Meng Po was waiting there, handing a bowl of Mengpo soup to every passer-by. There is a stone called Sansheng Stone by the Wangchuan River. Drinking Meng Po Tang makes people forget everything.