Holocene terrace along Niobrara River

Riffle at Fritz's Island, where the channel of the Niobrara River is eroded within Tertiary strata. Active channel sediment is locally sparse. Tertiary bedrock exposed on the bank is overlain by thin late Holocene sediment to form a low terrace that reflects a somewhat different and more sediment-rich channel system at the time the river was at the slightly higher grade.