Campbell County was named either for John Allen Campbell, a governor of the Wyoming Territory or for Robert Campbell, an early trapper, who was a fur trader associated with William Henry Ashley.
This led to the first exploration of the Green River, by William H. Ashley, one of the organizers of the Rocky Mountain Fur Company.
General William Henry Ashley had crossed the Laramie Plains in 1825, John C. Fremont camped near Elk Mountain in 1843 and miners and trappers heading to California used the Cherokee Trail in the late 1840s.
William Henry Ashley (1778–1838), American fur trader, entrepreneur, and politician
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Literary references to Thunder Butte appear in the story of Hugh Glass, a mountain man/trapper with the 1823 party of William Henry Ashley and Andrew Henry, which was traveling overland from Fort Kiowa to Fort Henry at the mouth of the Yellowstone River.