The chalk formed from the accumulation of coccoliths from microorganisms living in what was once the Western Interior Seaway, an inland sea that divided the continent of North America during much of the Cretaceous.

Evidence of vertebrate life is common throughout the formation and includes specimens of plesiosaurs, mosasaurs, pterosaurs, and several primitive aquatic birds.

Excavations continued through the following years up to 1879 under the direction of professional fossil collectors such as B. F. Mudge and S. W. Williston appointed by Marsh.

This dichotomy is not indicative of different stratigraphic units as was previously thought, but rather is seen as a weathering phenomenon that can be found at varying points in the same outcrop.

Re-exposed during the Quaternary,[4] these cherty materials, known as Smoky Hill Jasper and Smoky Hill silicified chalk, or more recently as Niobrara Jasper or Niobrarite, became source material for stone tools from the earliest human habitation of the High Plains.

[7] The Fort Hays member was historically quarried on the High Plains for the manufacture of Portland cement at Superior, Nebraska, and Yocemento, Kansas, as well as along the Dakota Hogback in Colorado from Lyons to Boulder, and around Pueblo and Florence.