Although preserved for its cultural significance, Fort Bowie NHS also encompasses a variety of natural features - such as springs, faults, and numerous soil types - which result in the wide array of flora and fauna found here. The Apache Pass fault, a visible fissure which can be seen on the Overlook Ridge Trail, is the source of the water that rises up into Apache and Siphon springs. The fault was formed when a block of limestone was overthrust and then folded over a block of granite, which are the two major rock types found here. Helen's dome, a mostly bare tower of granite, served as a landmark for travelers approaching Apache Pass.