The real highlights of Castle Rock are its beautiful views and imposing rock formations. On a clear day from certain trails in the park you can see across Walnut Creek, Concord, Martinez and the Carquinez Straight to Benicia, CA about 14 miles away. The rock formations in Castle Rock are composed of sandstone. There are sheer cliff faces, caves and outcroppings. The views from the tops of the rock formations often include hawks, falcons and other birds gracefully gliding through the winds.