SAN ANTONIO Investigators are working to determine the cause of a fire on the citys West Side early Wednesday morning. The fire was called in around 1:30 a.m. in the 300 block of North General McMullen Drive, not far from West Commerce Street. Firefighters said they arrived to find a portable building on fire next to a church. The portable building was likely being used as storage, fire officials said. The cause of the fire is not currently known.