What is the Priest's Trail in the novel, Thunderhead?

Priest's Trail is an ancient path over the edge of the canyon where Quivira is located. This is a secret trail that serves as a sort of back door to Quivira. This trail is so old and narrow that it is almost impossible to see and will not allow horses across. The skinwalkers use this trail to torment the expedition while Beiyoodzin uses it to rescue Nora and Smithback.