How did the surname "Ru" come from Pingliang City, Gansu Province?

From taking place names as surnames. After Zhou Pingwang moved eastward, he sealed his youngest son in Ruzhou and called him Ruhou. The descendants of Ruhou took the fief as their surname, and you were their surname from generation to generation. This is the main branch of your surname.

Pingliang belongs to the birthplace and important area of pre-Qin culture, and your surname should belong to ancient immigrants.