(CNN) -- California's massive Rim wildfire began when a hunter "allowed an illegal fire to escape," investigators with the U.S. Forest Service announced Thursday.
The hunter was not identified, pending further investigation, the forest service said, and no arrests have been made.
The fire began August 17 and grew to more than 237,000 acres, making it the fifth-largest in state history. As of Thursday, the fire was 80% contained.
Although the fire has consumed tens of thousands of acres inside Yosemite National Park, it has so far had little or no direct impact on Yosemite Valley, a popular spot for tourists and home to many of the park's iconic attractions, including the El Capitan rock formation.
Authorities had speculated that illegal marijuana growers could have accidentally started the fire, but the forest service said Thursday that "there is no indication the hunter was involved with illegal marijuana cultivation on public lands and no marijuana cultivation sites were located near the origin of the fire."