In the weird-ways-to-start-a-fire department, the 800-acre Lighthouse Fire last month was caused by two boulders. According to Utah state fire investigators, the fire started July 18 when a boulder fell 800 feet from a cliff face, bounced several times, then collided with a larger boulder and came to “an instantaneous stop.” Jason Curry, spokesman for the Utah Division of Forestry, Fire and State Lands, told the Deseret News that it’s a rare incident.

The boulder was about the size of a refrigerator, and it smacked a boulder the size of a sport utility vehicle. Curry said the pressure friction generated heat, which set off the fire in dry grass and brush.