Marshall started work in 1925 with the Forest Service, where he worked until 1928. Although he had hoped to go to Alaska, he was assigned that year to the Northern Rocky Mountain Experiment Station at Missoula, Montana. Marshall's research at the experimental station focused on the dynamics of forest regeneration after fires. He had to fight a widespread fire after a July storm started more than 150 fires in Idaho's Kaniksu National Forest. He was put in charge of supporting and provisioning one of the crews led by the Forest Service. As he later recalled, Marshall worked "18 to 20 hours a day as time-keeper, Chief of Commissary, Camp Boss, and Inspector of the fire line". Spending time with loggers and fire fighters, and seeing the conditions under which they worked, Marshall learned vital lessons about labor issues and natural resource use. At the experimental station, Marshall became interested in the unsafe conditions for many working Americans. He began to develop liberal and socialist philosophies.