Utah Division of Forestry, Fire and State Lands spokesman Jason Curry called the conclusion on the cause of the Lighthouse Fire "a rare one."
He tells the Deseret News a boulder the size of a refrigerator fell 800 feet from a cliff face on July 18 and bounced several times before crashing into a boulder the size of an SUV. Investigators say the impact created "pressure friction" so hot that it ignited grass and brush nearby.
The fire was contained four days later.
The Lighthouse Fire was in Range Creek, which is known for prehistoric Native American archaeological sites. None of those sites has been reported damaged.
Information from: Deseret News
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