The Cook-Folsom-Peterson Expedition of 1869 was the first organized expedition to explore the region that became Yellowstone National Park. The privately financed expedition was carried out by David E. Folsom, Charles W. Cook and William Peterson of Diamond City, Montana, a gold camp in the Confederate Gulch area of the Big Belt Mountains east of Helena, Montana. The journals kept by Cook and Folsom, as well as their personal accounts to friends were of significant inspirational value to spur the organization of the Washburn-Langford-Doane Expedition which visited Yellowstone in 1870.