The flames had plenty of fuel. Contra Costa fire officials say it started at Piedmont Lumber Company before spreading to Wally's Rental Center next door.
"Normally, when the alarm company calls it's a broken window or something of that nature. When they indicated that the fire department was here and the store was on fire I was quite concerned," Dave Ewald told ABC7.
"The structures are substantial because they carried a lot of weight. They held a lot of lumber and the buildings themselves were made of wood. So, it doesn't surprise me that they burned fast and hot," said Rob Myer of Piedmont Lumber.
Crews were able to contain the fire after a little more than an hour. They are still not sure exactly how it started. Damage has been estimated at about $500,000.