The Chisos Mountains were created by volcanic activity during the Eocene Epoch 35–44 million years ago.[3] The highest point in the Chisos Mountain range is Emory Peak at 7,825 ft (2,385 m) above sea level.The range of mountains extends twenty miles from Punta de la Sierra in the southwest to Panther Junction in the northeast.An extensive trail system and permit-required backcountry campsites are maintained by Big Bend National Park for its visitors.Two Mexican towns (Boquillas and Santa Elena) border the park; and cross-border access was reopened in 2011.