Diamond Valley Lake is a man-made off-stream reservoir located near Hemet, California, United States.

Excavation of core materials for the dams resulted in many paleontological finds, all of which are displayed at the Western Science Center at the lake's East end.

The location was also chosen because of its proximity, about 5 miles (8.0 km), to the existing Colorado River Aqueduct that originally supplied the lake with water.

[7] Construction of the three dams was completed in 1999, requiring the excavation of 31,000,000 cubic metres (41,000,000 cu yd) of foundation material.

It spans 1.5 miles (2.4 km) over a nearly flat alluvial valley floor between bedrock abutment ridges.

The foundation excavations were extended 90 feet (27 m) below the original ground surface to remove liquefaction soils that would have made the dam unstable in an earthquake.

Before embankment of the dam could begin, more than 18,000,000 cubic yards (14,000,000 m3) of alluvium had to be excavated to reach a solid bedrock foundation.

The Saddle Dam rises 130 feet (40 m) above the lowest point in the Domenigoni Mountains ridgeline of the north rim and is around 0.5 miles (0.80 km) long.

The dam was built to increase the storage capacity of the lake, which would have been limited due to the lower ridge in this area.

[3] Filling of the lake began in 1999 with water from the Colorado River Aqueduct and San Diego Canal.

[8] In 2001, four of the twelve pumps were converted to hydroelectric turbine generators capable of producing 3 megawatts of power each.

[12] During excavation, bones and skeletons were found from extinct mastodons, mammoth, camel, sloth, dire wolf and long-horned bison.

Paleontologists from the San Bernardino County Museum in Redlands, California uncovered thousands of fossils in the Diamond and Domenigoni valleys that will add immensely to the store of public knowledge about the region.

[13] The paleontological finds of mammoth, mastodon, bison, and other Pleistocene Epoch species from Diamond Valley Lake provide a unique snapshot on inland southern California during the Ice Ages, and bridge a massive information gap between fossil deposits at La Brea Tar Pits in Los Angeles, California and Ice Age sites in the Mojave Desert.

One of the most common animals identified from the Diamond Valley Lake site by San Bernardino County Museum scientists was the extinct American mastodon, Mammut americanum.

The reserve is home to at least 16 sensitive, endangered or threatened native California bird, animal and plant species.

[15] Stocking of the lake with fish began before the reservoir was filled, with a small rearing pond being placed on the bottom of the valley.