Refers to a narrow, deep canyon which forms part of the headwaters of Genowlan Creek. It is located 500m north, north east of Genowlan Trig Station. Named by Bruce Mullaney, a bushwalker with the Central West Bushwalking Club, in 2001. When he gazed down from the top rock platform into this hidden canyon, it looked prehistoric. Note this feature had been previous named as (see) Hidden Valley.