Badlands are a type of arid terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water. It can resemble malpaís, a terrain of volcanic rocks. Canyons, ravines, gullies, hoodoos and other such geological forms are common in badlands. They are often difficult to navigate by foot. Badlands often have a spectacular colour display that alternates from dark black/blue coal stria to bright clays to red scoria.
Some of the best-known badland formations can be found in the United States and Canada. In the U.S., Makoshika State Park in Montana, Theodore Roosevelt National Park in North Dakota and Badlands National Park in South Dakota together form a series of extensive badlands formations. Another popular area of badland formations is Toadstool Geologic Park in the Oglala National Grassland of northwestern Nebraska. The Big Muddy Badlands in Saskatchewan, Canada gained notoriety as a hideout for outlaws. There is a sizable badland area in Alberta, Canada, particularly in the valley of the Red Deer River where Dinosaur Provincial Park is located. The Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and Dinosaur National Monument in Utah are also badlands settings, and exhibit fossils found in the area. A small badlands called Hell's Half-Acre is present in Natrona County, Wyoming. It is famous as one of the locations for the filming of Starship Troopers (1997).
Arguably the most well known badlands formation in New Zealand, the Putangirua Pinnacles – formed by the erosion of the conglomerate of an old alluvial fan – are located at the head of a small valley near the southern tip of the North island. A famous European badland is the Accona Desert near Siena, Italy.