Officials have determined that a Northern California wildfire that consumed 43 homes last year was caused by an illegal cannabis cultivation operation, as reported by the Associated Press.

The blaze’s culprit was a makeshift water heater which the growers had installed near their 100 plant farm. “It was strapped to a tree. Quite inventive, and why it was not very safe,” California Department of Forestry and Fire Protection spokeswoman Janet Upton told the AP. The two suspects in the case fled the county, likely to avoid questioning.

The weed-induced “Rocky fire” was the second largest in the region last year, spreading throughout rural areas near San Francisco in Lake, Yolo, and Colusa counties, and destroying 43 homes and 53 outbuildings.

The vast majority of wildfires are caused by man-made missteps like this one. Another fire currently raging in the same area that Rocky scourged last year was caused by a serial arsonist. Of the nearly 5,000 California wildfires this year, 4,808 were caused by humans, over only 115 that were caused by lightning, according to the LA Times.

There are at least three major wildfires at work right now in the Golden State, including the Blue Cut fire, which this week caused 82,000 people to be evacuated from their homes just east of Los Angeles.

Photo via U.S. Fish and Wildlife Service