GLENDORA (CBS) — The Williams Fire raging in the Angeles National Forest since Sunday afternoon was 24 percent contained Wednesday, the U.S. Forest Service said.

The 3,600-acre fire is burning in an area that hasn’t seen fire in at least 15 years.

To encircle the blaze and prevent its spread, crews have to carve out containment lines over steep and unforgiving terrain in San Gabriel Canyon.

Seven firefighters have suffered minor injuries battling the blaze, but all were treated and returned to duty, officials said.

Full containment is not expected until Sept. 13.

No structures have burned.

The cause of the fire is under investigation.

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