Diamond Mountain National Forest was established as the Diamond Mountain Forest Reserve by the U.S. Forest Service in California on July 14, 1905 with 626,724 acres (2,536.26 km2). It became a National Forest on March 4, 1907. On July 1, 1908 a portion of Diamond Mountain was transferred to Plumas National Forest and the remainder to Lassen National Forest. The name was discontinued.
References
Diamond Mountain National Forest Wikipedia(Text) CC BY-SA