For untold generations, rivers served as the main travel routes for nomadic tribes and the earliest explorers. In 1872, the famed Far West became the first steamboat to travel up the Yellowstone River to its confluence with the Powder River, accompanying the first Northern Pacific Railroad survey team and carrying supplies for surveyors and soldiers sent to defend against hostile Sioux angered by encroachment that violated the 1868 Treaty of Fort Laramie. The railroad tracks through this area then helped draw heavy immigration. Later, a flash flood here caused one of the worst transportation disasters in twentieth-century American history when, in the early hours of June 19, 1938, a Milwaukee Railroad passenger train reached the Custer Creek Bridge just as torrential floodwaters struck it from below. The bridge collapsed, seven of the train's eleven cars fell into deep rushing water, forty-eight passengers were killed, seventy-five were injured, and forty-three survived unhurt. One car balanced for nearly an hour in total darkness before falling into the river and washing downstream. At the time, it was the second deadliest train wreck in U.S. history.