The rocks of the Catskill are predominantly red sandstone, indicating a large-scale terrestrial deposition during the Acadian orogeny.

Many beds are cyclical in nature, preserving the record of a dynamic environment during its approximately 20 million years of deposition.

This terrain was sandwiched between the epicontinental Kaskaskia Sea in central North America and the now-vanished Acadian Mountains.

Eventually, the Delta formation was buried and transformed into sandstone, which was then revealed in places when the Catskill and Appalachian Mountains were formed at a later date.

[1] Much of what formed the Catskills as they stand today is a result of the Wisconsin glaciation which ended only about 12,000 years ago.