Cook–Folsom–Peterson Expedition

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.

After crossing the mouth of the Gardner River, they traveled along the benches above the western side of the Yellowstone until they reached Tower Fall.

From Pelican Creek, Cook-Folsom-Peterson followed the western shoreline of Yellowstone lake closely until they reached the West Thumb area.

Turning northwest, they again crossed the divide and began traveling down the Firehole River into the geyser basins.

On the evening of October 11, 1869, Cook, Folsom and Peterson, after 36 days of travel returned to Diamond City, Montana.

While in that office, Cook and Folsom shared their experiences and diaries with Washburn and W. W. deLacy, the territorial map maker.

In their journals they did refer to many features incorrectly (based on incomplete or inaccurate maps made from previous accounts), thus causing some confusion that had to be sorted out by later explorations and surveys.