An average of two to five fortress villages in a small valley along a mountain stream, known in local Chinese as gou 沟, make up a village cluster (cun 村). The inhabitants of fortress village or village cluster have close contact in social life. In these small valleys, people cultivate narrow fluvial plains along creeks or mountain terraces, hunt animals or collect mushrooms and herbs (for food or medicine) in the neighboring woods, and herd yaks and horses on the mountain-top pastures.