Gouverneur K. Warren
In 1856 and 1857, Hayden accompanied exploration expeditions led by Lieutenant Gouverneur K. Warren and in 1859, the Raynolds Expedition of 1860 led by Captain William F. Raynolds, both of the Topographical Engineers. One result of which was his "Geological Report of the Exploration of the Yellowstone and Missouri Rivers in 1859–1860" (1869).