By Nick Janes

YOSEMITE NATIONAL PARK (CBS13) — As the Rim Fire burns into its third week, one official suspects the massive wildfire near Yosemite National Park was caused by an illegal marijuana grow.

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The Rim Fire has burned more than 235,000 acres, or more than 350 square miles—more than five times the size of Washington, D.C.

It’s 70 percent contained, but it’s still growing with more than 5,500 structures threatened.

Twain Harte Fire Chief Todd McNeil’s remarks ended up on YouTube, but flew under the radar for days.

“It started down in the brush. We know it’s human caused, there’s no lightning in the area,” he said. “Highly suspect it might have been some grow marijuana grow type thing.”

The U.S. Forest Service calls the pot grow possibility nothing more than a rumor at this point.

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The feds confirm to CBS13 that progress has been made on a case, but wouldn’t say anything else on their investigation into the fourth-largest fire in California history.

It’s worth nothing that in nearby Madera County, agents pulled out 15,000 marijuana plants from two grow sites in the Sierra National Forest.

A month before the raid, a fire erupted at one of the sites, blamed on Mexican drug traffickers. that fire was kept to 40 acres.

The Rim Fire has grown to more than 235,000 acres, torching land untouched by flames for decades.

“Like behind us here have been unburned since at least 1930s,” said retired research forester Jan Van Wagtendonk. “A fire gets into that, it’s going to be hotter, much more intense.”

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The forest services says it’s unclear when they’ll release findings on a cause.