Park Size. How large is Big Bend National Park? At 801,163 acres, Big Bend is the 8th largest national park in the lower 48 states, and the 15th largest in the U.S. Check out all the stats here. Pets. Are pets allowed in the park or on trails? Think carefully before bringing a pet to Big Bend. Pets will limit your experience in Big Bend to a certain degree. Pets are NOT allowed on trails or in the backcountry for the protection of the park, wildlife, hikers, and your pet. Pets are allowed anywhere vehicles can go, such as roads and primitive campsites, but pets must be on a leash and may not be left unattended.