Be prepared for unpredictable weather in the Black Hills [1]. While summers are generally pleasant and dry, temperatures can soar to over 100°F by afternoon and fall to 50°F in the evening. Caves maintain a temperature hovering in the mid-50s no matter the outside temperature. Wind on the plains can be brisk and strong.
Given these weather possibilities, be sure to think in layers when you pack. Cotton t-shirts work well on hot afternoons, layer with a long-sleeved shirt in the evening. Bring a windbreaker and pack a sweatshirt for cave tours and cool evenings.
Dressing in layers is also key to comfortable hiking. Be prepared for afternoon thundershowers and bring raingear. Even the shortest of hikes can be hard on the feet, and this is especially true in the Badlands. Bring sturdy, ankle-supporting footgear. Another must is sunscreen and sunglasses. And don’t forget the binoculars.
While a bathing suit might seem out of place in this landlocked region, many lodgings feature outdoor hot tubs, a very relaxing way to end a day, and there are many small lakes for swimming.
Dress is casual everywhere in the hills. You can dress up if you like, particularly in the finer restaurants, but jeans are welcome most everywhere.
Links:
[1] http://www.moon.com/destinations/mt-rushmore-the-black-hills/discover-mount-rushmore-the-black-hills