The prairie lies to you here. For mile after mile around Wall, South Dakota, the land rolls flat and grassy, with wheat fields, cattle and the long, straight line of Interstate 90, and nothing suggests that a few kilometres to the south the ground is about to fall away into a maze of eroded spires and canyons.
Wall is famous for one thing: Wall Drug, a sprawling roadside store that began in the 1930s by offering free ice water to thirsty travellers, and advertised it on signs for hundreds of kilometres in every direction. It worked, and the drugstore grew into a tourist attraction in its own right, with shops, restaurants, a chapel and an animated dinosaur. It is kitsch, but it is also a slice of American road-trip history, and the coffee is famously cheap. During the Sturgis Motorcycle Rally in August, the town is packed with bikes.
The ride south from Wall is short and easy, with gentle curves across the grassland. Then, quite suddenly, the road reaches the edge of the Wall, a long escarpment that gives the town its name, and the badlands appear below you. The first view is stunning: a vast expanse of jagged ridges, buttes and gullies, striped in bands of white, grey, pink and gold, stretching to the horizon.
The weather on the prairie is extreme. Summers are hot, with temperatures often above 35 degrees, and violent thunderstorms can sweep across the plains in the afternoon, bringing hail, lightning and strong winds. Winters are bitterly cold, with blizzards and icy roads. Late spring and early autumn are kinder, when the temperatures are milder and the light is softer.
Wall has fuel, food, lodging and all the basic services, and it is the best place to fill up before entering the park. Inside the park, services are limited, and fuel is not always available. Philip, about forty-five kilometres to the east, and Kadoka, further east along the interstate, have the basics, but Rapid City, about ninety kilometres to the west, is the nearest large town with everything you might need.