After you have toured the main points on the major park roads, you may want to see more by vehicle. You can do so on the primitive roads, which introduce further varieties of scenery and interesting plants, animals, and historic features. Plan your trip in advance, don’t just turn off a main road on the spur of the moment. And register at park headquarters, getting current information about road conditions from a ranger. On these primitive roads you are on your own, so play it safe. Primitive roads are patrolled only infrequently. Some are suited only for 4-wheel drive. A _Road Guide to Backcountry Dirt Roads of Big Bend National Park_ may be purchased at Panther Junction. [Illustration: Horse and rider in the hills] Persimmon Gap Drive. This drive offers short side trips: on a motor nature trail up to Dagger Flat, or just off the highway north of the Tornillo Creek bridge to the fossil bones exhibit. Signs along the Dagger Flat road identify Chihuahuan Desert species, including the giant-dagger yuccas, found in the United States only in Big Bend country. The Fossil Bone Exhibit shows an extinct mammal, _Coryphodon_, whose remains were found in sandstone deposits about 50 million years old. Tornillo Creek is one of the park’s largest drainages. The Chisos Mountains, seen as you approach Panther Junction, are the park’s highest. Panther Junction is such a focal point that you may overhear park employees call it PJ. Maverick Drive. Terlingua and Study Butte are ghost towns—or nearly so—which were once prosperous cinnabar (mercury) mining communities. The large, rounded Maverick Mountain north of the road near the Maverick entrance is the eroded exposure of an intruded mass of molten rock pushed up through softer, older rock beds. You will also see the Painted Desert and many plants of the desert shrub community. Outside the park to the north the Christmas Mountains are prominent. To the east the Chisos define the skyline. Along the Maverick drive you come to the Santa Elena Junction, where the Santa Elena drive begins (see below). Further on you will see dry washes that can carry flash floods and gravel slopes formed by the erosion of the mountains. Then you come to the Basin Junction, where the Basin drive begins (see below). Near this area you may also see mule deer, the peccary (or javelina), coyote, or other desert animals. The next stop—except for pictures—is Panther Junction. Boquillas Drive.