MULLEN, Neb. — About a dozen fire departments joined forces Thursday to battle a large grass fire south of Mullen.

Firefighters were called to Mule Deer Road early Thursday afternoon. By Friday morning, a plane was checking for hot spots, and the fire had been contained. Mullen Volunteer Fire Chief Tyler Cash said a Civil Air Patrol plane plans to map the burn area to determine the exact size, but a spray-plane pilot estimated it between 1,200 and 1,800 acres. Others on the ground thought it was much larger.

Cash said the cause is still under investigation, but authorities believe a pickup started the fire.

This marks the second significant grass fire in the area this month. As News Channel Nebraska reported last week, a fire north of Thedford — also sparked by a vehicle — burned more than 500 acres.

“With deer season starting tomorrow, people really need to be aware of the dry conditions,” Cash said.

The area is under a Red Flag Warning Friday because of high fire danger. The National Weather Service is forecasting record highs in the upper 70s to low 80s, with humidity expected to drop to around 15%.

“Any fires that develop will have a high probability for rapid spread and will be difficult to control,” the National Weather Service said in a press release.

In addition to the Mullen Fire Department, crews from Hershey, Sutherland, Heart of the Hills, Mid-Cherry, Hyannis, Thedford, Stapleton, Tryon, Halsey, Arthur and Valentine responded. Hooker County Roads, the Hooker County Sheriff’s Office, the McPherson County Sheriff’s Office and numerous ranchers also assisted.

“It’s dry, and people need to make sure their tanks are on even if they don’t have cattle out. There are a lot of dry tanks right now,” said Cash.