Theodore Roosevelt was a huge fan of North Dakota. Seriously. He spent quite a few summers in North Dakota's badlands on his ranch, the Maltese Cross, and later the Elkhorn Ranch. He was appalled by the destruction of our country's national resources, by over-grazing, over-hunting, and over-farming.
This inspired his move, once elected president of the United States, to declare 51 Bird Reserves, 4 Game Preserves, and 150 National Forests. He also established the U.S. Forest Service, signed into law the creation of 5 National Parks, and signed the 1906 Antiquities Act under which he proclaimed 18 national monuments. The area of the United States placed under public protection by Theodore Roosevelt totals approximately 230,000,000 acres.
After Roosevelt died in 1919, there were many places that were considered as memorials to the late commander in chief. The Little Missouri Badlands in North Dakota were chosen by Sylvane Ferris, a friend of Roosevelt's during his foray in the cattle business. After 20 years of litigation and 7 years of work by the CCC during the dirty thirties, Theodore Roosevelt National Memorial Park. This was comprised of the current south unit, and Elkhorn ranch site. A year later the north unit was added, and in 1978, the signed the law changing both units to Theodore Roosevelt National Park.
The south unit is located near Medora, and the north unit is located 50 miles north of I-94 on US-85. The main difference between the two areas is that the southern unit is much more tourist driven, and looks like typical badlands, with erosion carved buttes and the painted canyon. The north unit has a much more DIY feeling to it, with a minimum of facilities and support. It looks generally the same, but isn't quite as dramatic as the southern unit.
The Little Missouri river, a sediment-ridden trickle of water, and its feeding streams run through the south unit, and provides a vein of life. Along the banks of it are the only places you will see any fair amount of deciduous trees. Most other trees are Junipers found on the northern sides of hills, where the sun doesn't beat down quite as hard.
Trees don't grow out everywhere because there is so little rain during the year. Some experts classify western ND as an arid steppe type of climate, with hot summers, cold winters, and little precipitation, which doesn't allow for growth of much but grass. Accenting the seas of prairie are prickly pear, creeping juniper, and a variety of wild flowers and herbs, such as echinacea, clover, wormwood, and purple coneflowers
The animal life in the park is more visible than anywhere else in the state. There are herds of bison throughout both units. If you don't see a bison on your visit, you aren't looking. Also prairie dogs are common in "towns" throughout the park. Locals will tell you, "Some silly easterners think are endangered." One of the state's few populations of bighorn sheep, and some bands of rarely seen mustangs can also be spotted in the southern unit.
As far as reptiles, some rattlesnakes have been spotted, but actual incidents are few and far between. you are much more likely to see a bull snake, which looks and behaves similarly, but lacks a rattle and venom.
Overall, the park is truly a treasure. In the middle of nowhere, with a wonderful system of trails, including the mammoth Maah Daah Hey trail, which is over 100 miles long and connects both units. You can get a true appreciation for the countryside, and see what drew the 26th president here in the first place.
http://www.nps.gov/thro/, and my own experiences.