The story of the Western Center began over 230,000 years ago after the Pacific Ocean had receded and Southern California's inland valleys were covered with lush vegetation. As the climate dramatically changed, the secrets of life in these valleys were buried in an arid landscape where they remained hidden until the digging began.

In 1995 Metropolitan Water District (MWD) began construction on the 4,500 acre Diamond Valley Lake in Hemet. At four and one half miles long by two miles wide, and costing over $1.5 billion, this reservoir was the largest civil engineering project in the United States and is the largest man-made freshwater lake in Southern California. Large-scale excavations for the massive project led to the discovery of some of the most significant Ice Age fossils and Native American artifacts in the Western United States.

Paleontologists and archaeologists discovered astonishing treasures as they worked alongside construction crews an engineers. The earth revealed such an unprecedented collection of mastodons that scientists began calling the site the Valley of the Mastodons. Among the fossils uncovered were "Max" - the largest known mastodon in the Western United States, and "Little Stevie" - a young mastodon that is the most complete ever recovered in the inland region of Southern California. An amazing array of fossils shed light on long-extinct animals previously unknown in the region.

In addition, archaeologists discovered over 300 Native American sites with documentation of human life in the valleys from the Ice Age to the present. It was here that scientists discovered the oldest piece of pottery in the Western United States, verified by the Smithsonian Institute to be approximately 9,000 years old. In all, the collections comprise nearly 1,000,000 artifacts and fossils.