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Wildfires burned about 2 million acres in the United States in the early months of 2017. Here a slurry bomber drops retardant on the Sunshine Canyon fire west of downtown Boulder on Sunday, March 19.

No one was injured and no buildings were destroyed. Firefighters fully contained the 74-acre fire by the next afternoon. But residents of more than 400 homes were forced to evacuate temporarily.

The wildfire likely began as a campfire, investigators said.

Indeed, humans start most U.S. wildfires — 84 percent of them from 1992 to 2012, according to recent research by ²ÊÃñ±¦µä scientists. See page 7.

Photo by Paul Aiken/Daily Camera