RAMONA, Calif. -- Officials are investigating a series of brush fires that broke out within two hours in East County on Friday.

The first fire, deemed the Ash Fire, broke out in around 11:50 a.m. near Ash and Maple streets, off state Route 78, according to Cal Fire. The fire briefly threatened ten nearby structures, officials said. The blaze burned a total of 5 acres before it was contained.

Air tankers and 15 engines worked to contain the blaze, Cal Fire said.

Around 12:48 p.m., officials responded to a second fire near Valley Center. That fire, called the Mystery Fire, burned 12 acres of brush near Mystery Mountain Road and Old Castle Road. Structures were also briefly threatened but none were damaged or destroyed, officials said.

The cause of the fire was equipment use, according to Cal Fire.

San Diego Fire-Rescue crews and Cal Fire worked together to battle the Poway Fire, which started at 1:45 p.m. That blaze, located at Highway 67 and Poway Road burned 2 acres, officials said.

The cause of all three fires is under investigation.

A separate smaller fire broke out in Santee, according to the San Diego Sheriff's Department. It was burning near Woodglen Vista Drive and Magnolia Avenue.

Cajon Park Elementary School, located at 10300 N Magnolia Ave., was in "fire-drill mode" for possible evacuation, per the sheriff's department. If the fire had become a threat, the school would have been evacuated, officials said.