The North Slope is mostly tundra peppered with small villages. The area is known for its massive reserves of crude oil, and contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field. Barrow, the northernmost city in the United States, is located here. The Northwest Arctic area, anchored by Kotzebue and also containing the Kobuk River valley, is often regarded as being part of this region. However, the respective Inupiat of the North Slope and of the Northwest Arctic seldom think of themselves as one.