The two founders of the village, the unnamed Hyuuga and A woman who was capable of manipulating the nature around her traveled to a far location inside of the Sand Village domain*never entered the sand village* It was there that These two, as well as a group of 400 Jounin rogue shinobi started the Mountain Village. The woman used many different hand signs to create a great tunnel into the mountain and surrounded the area with thick trees and brush creating a maze so no other person could find the entrance to the village