Why do many ancient poems mention "Bashan"

Bashan "refers to Daba Mountain in Sichuan and the area around the two lakes. The amount of night rain in these places generally accounts for more than 60% of the annual precipitation, and the meaning of rain in China's classical poems is lonely and sad. There is also Li Shangyin's poem "The Desolate Land of Bashan and Chushui", so later generations use the late rain to describe the lonely scene of being unfamiliar with life and lingering in the rain every night. The Bashan in Liu Yuxi's "Bashan Chushui Desolate Land" refers to the place where he was relegated, and there is also a feeling of sadness and loneliness.