Welcome to Tai'an Hot Springs
As you drive up County Rd 62, the people you see at the start will be almost exclusively Hakka, while further inland Atayal people predominate. (Tai'an is in fact the last remaining Atayal area with elderly women who have facial tattoos; the last Atayal man with tattoos died in 2013.)
This pattern is common in mountainous regions in Taiwan. As late immigrants to Taiwan, Hakka groups often found the best land on the plains long settled. By purchase or pressure, Hakka groups acquired their share, often causing indigenous groups to move further into the mountains.