Big Bend National Park

Falcon Guides is a great guide to the hiking trails in the park.  It has hikes from beginner to difficult.  The intro chapters provide good basic information on the challenges of hiking in such a challenging environment.

More than a hiking guide.  While the guide contains info on hiking and outdoor activities, it also contains sample itineraries, guidance on clothing, and what to keep in the car for safety. 

National Geographic Trails Illustrated maps are among the best for all but those venturing into the backcountry and wilderness.  The accompanying day-hike guide lists numerous shorter hikes ranging from beginner to advanced. 

Despite being in a desert, there is plant life can thrive.  This book covers 75 native plants in detail - from trees and shrubs to cacti and succulents.   A good guide to understanding the flora of a large part of the park.

A rare paleontological guide to a park.  This book covers the basics of the geological history but details what type of fossils exist in which areas.  For instance, the Boquillas area was once under the inland seas, so marine fossils are predominate in the area.

This is an older book so some of the information on services and park rules might be out of date.  However, most of the book is  still very relevant.   The guide covers both the geological and more recent history of the areas as well as the various ecosystems in the park. While the park is predominantly desert, the elevation change leads to a more diverse environment than one would think.