Over time, rivers erode the land beneath them as they flow, picking up lighter sediments and carrying them downstream. Over thousands of years, more and more material is carried away by the constant flow of water, making a river deeper and wider. In some cases, the erosion can be so extreme that the river actually carves a deep, wide path into the ground below. These erosion-born pathways eventually become valleys, and if they can grow deep and steep enough, even canyons and gorges.
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