Sediments and Fossils

The rock layers in the bluff across the river are made of sediments—particles of sand, silt, and clay—carried by the ancient Snake River and deposited as the river entered an ancient lake. These layers, called strata, usually formed slowly over many years, building up only a few inches at a time, though floods could create strata rapidly and often trapped plants and animals within the sediments. Fossils, which are traces or remnants of organisms from the geologic past, are buried in these layers, and bones become fossils when their organic cells are slowly filled or replaced with minerals. Fossils found here include mammals, birds, fish, reptiles, amphibians, and plants that scientists have dated from three to four million years old.

Hagerman, Idaho · United States