This material included quartz and feldspar from Precambrian granite, but also residue from the uplifted shale, limestone, and sandstone accumulated from the Paleozoic and Mesozoic periods, as well as igneous rock from Cenozoic volcanism.

Owing to the low amount of sloping, vast quantities of sand and gravel were dumped on the plains in broad and overlapping alluvial fans rather than being carried into the Mississippi River.

[3] From bottom to top, the Ogallala was deposited as overlapping alluvial fans of sand and gravel, displaying bedding resulting from river flows and flooding.

Patterns of thin lines in the "limestone" suggested algal origin to frontier geologists (calcite and silica deposited within mats of algae under a shallow lake).

[6] The lowest, oldest deposits filled in the shallow valleys of the weathered rocks that were exposed at that time,[7] which ranged in age from Cretaceous in Nebraska and Kansas to Permian in Texas.

As the rivers built up the alluvial fans, subsurface water circulation varied, resulting in localized formation of caliche, and shallow lakes formed between natural levees, which deposited limestone.

Faced with particularly rich collections of terrestrial Neogene vertebrate fossils, Nebraska geologists recognized the distinct North American land mammal ages (NALMA) within the Ogallala; Clarendonian, Hemphillian, and Blancan sufficient to attempt definitions of formations on a biostratigraphic basis.