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It’s a news alert that California has seen too many times this year: a fire starts and grows to thousands of acres within hours.

On Thursday it was the Delta Fire, which raged in forests thick with conifers along the steep slopes of the Sacramento River valley north of Redding. Moving north through thinly inhabited areas, no homes were burned as of late Thursday and there were no reported injuries or deaths, according to Chris Losi, a public information officer for the Shasta Trinity National Forest.

But the fire closed down Interstate 5, the crucial artery connecting California to the Pacific Northwest. And it was moving very fast: The fire ignited Wednesday and by Thursday evening 22,000 acres had burned.

“The fire is behaving aggressively,” Mr. Losi said. “In some places 300-foot flames have been observed.”