An ancient (110 Million Years) shoreline that runs through the vicinity of the Cibolo Creek locality, of which Cascade Caverns Park and its caves are a part, was formed from a lower Cretaceous reef. This reef was dominated by two organisms at the time of fossilization, caprinid rudistids and star corals. The carpinids are most apparent in fossil form because of their long horn-like body shape. When living, these clams secured themselves to the sea floor through a lower valve and opened a lid on the upper valve opening to allow filter feeding off of nutrient rich waters.

The formations containing the fossils of these organisms occur in many locations on site as well as in the cave. They appear as tusks or fossilized roots when exposed on their sides or perfectly round rings when exposed upon their tops.

In the first room of Cascade Caverns directly opposite the main door is evidence of a portion of this coral reef in the form of fossilized star corals and rudist caprinids, as well as many oysters shell fossils.