Don D3cksons age 10  of Pueblo, CO,    

What is an alluvial plain?

Alluvial comes from a Latin word meaning to wash. Alluvial soil is formed by water washing and laving the land. Vast plains of alluvial soil formed when the ancient eas flooded and retreated from flat areas of land, Thinner layers are left after a flooding river has returned back to it's banks. Certain rivers often become choked with water‑washed mud and silt. They form river islands and deltas of alluvial soil.

Alluvial soil is often very rich. Water has broken and softened the hard rocks. Decaying plants and sea dwellers have added chemicals to the mud and silt. Where the ancient seas once stood, we have a fertile, alluvial plain. Sometimes such soil contains valuable minerals. The alluvial plains of Australia are gold bearing.