Nittany Mountain is part of a synclinal depression of the anticlinal Nittany Arch, which originally formed a huge mountain, since eroded, that towered over what is now Nittany Valley. The present Nittany and Big Mountain ridges were originally a valley in this ancient mountain. The Nittany ridge line is topped by the erosion-resistant Bald Eagle Sandstone. The more durable Tuscarora Quartzite formations are found exposed on the higher ridges of the northern end of the same syncline: Big Mountain to "Riansares Mountain" and Big Kettle Mountain to "The Winehead". The more easily eroded Juniata Shale forms the depression between the lower and higher ridges, and the drainage from this area cut small ravines in the Nittany ridge line. The same three rock layers are exposed in the neighboring ridges.
