Adam Ruelas of the Mill Creek Hot Shots lights a backfire as they battle a wildfire near Big Bear, Calif., Tuesday, June 20, 2017. Mandatory evacuations have been called for homes as a wildfire burns in the San Bernardino Mountains east of Los Angeles. (James Quigg/The Daily Press via AP)

Members of the Mill Creek Hot Shots prepare to battle a wildfire near Big Bear, Calif., Tuesday, June 20, 2017. Mandatory evacuations have been called for homes as a wildfire burns in the San Bernardino Mountains east of Los Angeles. (James Quigg/The Daily Press via AP)

A tree and power pole are consumed by a wildfire near Big Bear, Calif., Tuesday, June 20, 2017. Mandatory evacuations have been called for homes as a wildfire burns in the San Bernardino Mountains east of Los Angeles. (James Quigg/The Daily Press via AP)

In this Tuesday, June 20, 2017, photo, provided by Ann Alden shows a wildfire, locally called the Encino Fire, in Sonoita, Ariz. An extreme heat wave in the Southwest U.S. made the fight against a series of wildfires more difficult Wednesday. (Ann Alden via AP)

This photo provided by Ann Alden shows the Encino Fire in Sonoita, Ariz., Tuesday, June 20, 2017. An extreme heat wave in the Southwest U.S. made the fight against a series of wildfires more difficult . (Ann Alden via AP)