What is typically found below floodplains?

Bedrock is typically found below floodplains because floodplains are often formed by the sediment deposition of rivers and streams over time. These floodplains are characterized by rich soils resulting from the accumulation of alluvial materials. As the floodplain sediments build up, they often rest on top of bedrock, which is the solid rock underlying the surface materials. Bedrock serves as the foundational layer below the more easily eroded and transported sediments found in the floodplain.

Other options, such as glacial till and pebble deposits, are specific to certain geological formations and processes and are not standard features found below floodplains. Additionally, while rich organic soil may be present within the floodplain itself, it typically does not occur below the floodplain, as the layer beneath would generally consist of geological materials such as bedrock rather than organic matter.