Topography refers to the physical features of an area. This includes any areas with a steep gradient versus a flat, level land mass. Water flows from high to low altitudes due to force of gravity. A young stream is the result of an uplifted land mass with running water on it which flows downhill. Since there will be a steep gradient, the water flow is rapid and this running water has the ability to erode the surrounding landscape in the downward direction. Water can transport sediments including broken down rock. These sediments can be transported far from their place of origin. As the land erodes, the stream creates a valley where the water runs through its lowest point. In a young stream, the valley has a characteristic V-shape with steep sides. Young streams have not yet formed a flood plain--a wide area at the bottom of the valley that is level. This occurs later on in stream formation. As more land is eroded by the flowing water of the stream, the valley will widen and as it ages, it becomes U-shaped. The gradient is less steep due to erosion when a stream is more mature. The sides are now sloped and this can lead to the floodplain formation characteristic of older streams. Once the stream is established over a long period of time, it is considered an older stream. Erosion has established broad and gently sloping rather than steep hills, the water flows much more slowly and has a tendency to flood.