CAL FIRE investigators were immediately dispatched to the Glass Fire and began working to determine the origin and cause of the fire. After a very meticulous and thorough investigation, which included months of follow-up on information provided by the public, not enough evidence was available to conclusively identify the cause. The cause of the Glass Fire is currently Undetermined pending any additional information or evidence that could lead to the determination of the cause.
Tinder dry vegetation and strong winds combined with low humidity and warm temperatures contributed to extreme rates of fire spread which contributed to the difficulty in determining the cause of the fire.
Source: CAL FIRE