 An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain.At Bourne sections have shown highly weathered gravels overlain by sandy silts and clay loams, the highest levels in the sequence
showing evidence of cryoturbation.Two phases of fan sediment deposition were separated by a long period of subaerial weathering, which may represent an interglacial period.