Alluvium generally refers to the clay, silt, sand and gravel that are deposited by a stream, creek or other water body.  Alluvium is found around deltas and rivers, frequently making soils very fertile. Alternatively, “colluvium” refers to the accumulation at the base of hills, brought there from runoff (as opposed to a water body). The Oxnard Plain in Ventura County is a visible alluvial plain, where floodplains have drifted over time due to gradual deposits of alluvium, a feature also present in Red Rock Canyon State Park in Kern County. Similarly, alluvial fans are fan-shaped formations created from alluvium deposits, with the narrow end facing the water body depositing the sediment, often at the mouth of a canyon.