With the air in the Santa Clarita Valley thick with smoke from the Lake Fire Tuesday morning, fire officials announced the blaze had grown to 21,115 acres, while containment remained at 38%.

Overnight, firefighters continued to make steady progress on the blaze, tackling the steep, rugged terrain that continues to challenge them as they work to build containment lines. One firefighter has been injured battling the fire.

The blaze, dubbed the Lake Fire after it began in the Lake Hughes area on Wednesday, continued to threaten 4,570 structures Monday, while no additional structures had been damaged. In total, at least 12 structures and 21 outbuildings had been destroyed, along with three structures damaged.

Angeles National Forest and L.A. County Fire Department officials remain in unified command, with assistance from a federal incident management team.

As an extreme heat warning remains in effect until Saturday, with the National Weather Service forecasting high temperatures ranging between 102-111 degrees, along with high relative humidity, fire officials expect it to bring critical fire weather to the region. Full containment of the fire is not expected until Sept. 2.

Evacuations remain in effect for Lake Hughes Road, west of Pine Canyon and north of Dry Gulch Road; east of Ridge Route Road; west of Lake Hughes Road and Fire Station 78; north of Pine Canyon and Lake Hughes Road; and south of Highway 138.

3 Points Road from Highway 138 to Pine Canyon, Old Ridge Route from Highway 138 to Pine Canyon, Pine Canyon from Ridge Route Road to Lake Hughes Road, and Dry Gulch Road from San Francisquito Canyon Road to Lake Hughes Road remain closed.

In addition, both upper and lower Castaic lakes remain closed through the duration of the fire, as firefighters are using the lake and surrounding areas as a base camp.

The L.A. County Board of Supervisors met Tuesday in a special meeting to ratify the proclamation of a local emergency for the Lake Fire, submitted by Supervisor Kathryn Barger, whose 5th district includes the SCV.

“The Lake Fire has been fast-moving and tenacious, fueled by unforgiving terrain and burned 10,000 acres in just under four hours with minimal wind conditions,” Barger said. “I’m grateful for the tireless hard work and dedication of the firefighters in the Los Angeles County Fire Department, along with the U.S. Forest Service and Cal Fire. We have many days ahead, and I know for them their efforts to gain control in the Lake Fire is front and center, and we appreciate their support.”

The motion, which passed unanimously, is expected to enable the county to more effectively respond to the blaze, accelerating the procurement of vital supplies, mutual aid, and potentially obtain reimbursement and assistance from the state and federal government.