Set along the banks of the Big Sioux River, Sioux Falls is the biggest little city in the region. In fact, the Gateway to the Plains is larger than any other city in South Dakota, North Dakota, Wyoming, or Montana. Sioux Falls takes its name from scenic cascades formed 14,000 years ago as Ice Age glaciers retreated. The shifting ice also exposed pinkish, quartzite bedrock, which was used to construct many of the city's older buildings. The prominent river provides many benefits to locals. A good portion of residents are avid outdoors people who camp and hunt on its banks and fish and canoe its winding course. Tapping into this contingent, the city's Outdoor Campus (a joint venture between the Parks and Recreation Department and the Fish and Game Department) offers classes in boating, fishing, and wilderness exploration. In addition to waterways, Sioux Falls boasts extensive greenways: the city maintains more than 16 miles of biking and walking trails, which are given frequent use by visitors and locals alike.