YAKIMA, Wash -- A large wildfire is burning amid the grass and sagebrush of the military's Yakima Training Center in Washington state.

The fire grew to 50 square miles Friday morning but was not threatening any structures.

Fire spokesman Rick Acosta said the fire is being driven by winds through steep, rugged terrain. About 200 firefighters and several helicopters are battling the blaze.

The fire is about 15 miles east of Interstate 82 on the sprawling military training range.

Acosta said it started Wednesday, and the cause is under investigation.

-- The Associated Press