Colder weather, bringing with it rain and snow on September 11, calmed the fires down substantially throughout the Greater Yellowstone Ecosystem. Though the fires continued to burn well into the middle of November, they never again posed an immediate risk to life or property. Many fire crews were sent home, but additional manpower continued to arrive at Yellowstone to rehabilitate areas that had been affected by the firefighting efforts. Hundreds of miles of firelines, helicopter landing zones and fire camps needed to be restored to a more natural state, and thousands of hazardous dead trees needed to be cut down to protect roads and buildings. Finally, on November 18, all fires in Yellowstone were officially declared out.