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 (129 square kilometers) on Friday morning, but was not threatening any structures.

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

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

Acosta says it started on Wednesday and the cause is under investigation.