devastating forest fire that torched 3 million acres (1.2 million hectares) in western Montana and northern Idaho during Aug. 20–23, 1910. Of the fire's 85 victims, 78 were firefighters.

After record low precipitation in April and May 1910, severe lightning storms in June ignited numerous fires in the mountainous forest region between Montana and Idaho. Throughout July the fledgling U.S. Forest Service, created by Pres. Theodore Roosevelt (Roosevelt, Theodore) in 1905, employed roughly 4,000 firefighters to combat the fires. With the help of military reinforcements, the Forest Service seemed to have the situation under control, but on August 20 a dry cold front brought strong winds into the region. Winds of up to 70 miles (110 km) per hour whipped the flames into a frenzy as individual blazes united to form a massive conflagration. Balls of fire shot into the air, and firebrands fell as far as 50 miles (80 km) away. The fire spread so quickly that many firefighters were forced to seek shelter in creeks and mine shafts. On August 23, rain finally fell over the area, and the fire came under control.

In 1910 two fire-control strategies competed for prominence in the United States: one group argued that fires were a vital part of forest ecology, while Roosevelt's conservationists (conservation) contended that fires served no purpose and should be entirely prevented. The devastation caused by the Big Blowup resulted in the adoption of a “no fires” policy—a strategy that, by allowing an increasingly dense growth of trees and underbrush, actually led to larger fires in the future.