SAN DIEGO - A fire at a Mira Mesa construction-materials processing plant sent a thick column of smoke into the air Friday afternoon until crews could quell the flames.

The blaze at the Vulcan Materials Company building in the 10000 block of Black Mountain Road erupted for unknown reasons shortly before 3:30 p.m., according to the San Diego Fire-Rescue Department.

It took about two dozen firefighters roughly 20 minutes to smother the flames burning over asphalt and other materials, SDFRD spokesman Maurice Luque said.

Investigators were working to determine what sparked the blaze, which began inside the second level of a structure and spread outside.