In 1980, a group of Northern Arizona University students and their instructor were searching for fossils in the Verde formation when they discovered the remains of a stegomastodon near the Clarkdale Cement Plant. By all indications the animal died on the shore of ancient Lake Verde about 2.5 to 3 million years ago.

The discovery of the mastodon and the unearthing of mammoth bones in Camp Verde, along with numerous discoveries of footprints left by ancient horses, antelope, camels and saber tooth tigers, are proof that the valley was a haven for some of the more familiar megafauna that roamed the earth during the Pliocene era