In early 1859, Raynolds was charged with leading an expedition into the Yellowstone region of Montana and Wyoming to determine, "as far as practicable, everything relating to ... the Indians of the country, its agricultural and mineralogical resources ... the navigability of its streams, its topographical features, and the facilities or obstacles which the latter present to the construction of rail or common roads ...".

Hayden, who led several later expeditions to the Yellowstone region, photographer and topographer James D. Hutton and artist and mapmaker Anton Schönborn.

Hutton was the first person of European descent to reach the rock formation in northeastern Wyoming, later known as Devils Tower; Raynolds never elaborated on this event, mentioning it only in passing.

[1][3][8][9] Hampered by towering basaltic cliffs and deep snows, Raynolds attempted for over a week to reconnoiter to the top of Togwotee Pass, but was forced south due to the June 30 deadline for reaching Three Forks.

[3][7] Though the Raynolds Expedition was unsuccessful in exploring the region that later became Yellowstone National Park, they were the first U.S. Government sponsored party to enter Jackson Hole and observe the Teton Range.

[3] Overshadowed by subsequent larger events where the nation's objectives were turned away from western exploration and expansion, the geological, cartographical and historical importance of the expedition nearly vanished into obscurity.