Over 255 million years ago, a deep inland sea covered this land and mountains, and a large reef formed there. As the inland sea vanished, minerals such as calcite and aragonite bonded together the remaining sea life, helping create the unique mountains, canyons, and caves of the Guadalupes. Traces of that sea life, including sponges, algae, clams, and snails, may still be found in the Guadalupes.