"The fire burned right up to a couple houses up on Bernal Court," said Battalion Chief Mike Brown of the San Ramon Valley Fire Protection District.
"Cigarettes don't always do that, but in these conditions they can," he said.
Weather conditions have been dry and hot - at 10 percent humidity, which Brown called "very, very low." On Thursday afternoon there was a northwest wind making the risk even higher.
It took 24 firefighters about 20 minutes to contain the fire. Eight off-duty officers were called in to help fight the flames. Though the fire was small, the department wanted to be sure there was plenty of backup staff given the high risk conditions.