Updated

It's unlikely a fire burning in and around Yosemite National Park started at an illegal marijuana grow site, a federal forestry official said Wednesday.

Jerry Snyder of the U.S. Forest Service said that the steep and inaccessible canyon where the Rim Fire started Aug. 17 in the Stanislaus National Forest doesn't have a water source that growers look for when they set up remote gardens.

"I've heard many rumors, and that's one of them," Snyder said. "This isn't the kind of terrain growers look for. They want an isolated area, but they want access. This doesn't have it."

Snyder also said lightning isn't to blame. It could take months for investigators to determine what ignited the blaze that has consumed more than 370 square miles of Sierra Nevada forests.

"They'll be able to tell whether there was an illegal campfire in there," he said. "Another thing to consider is that this area is very steep, and if there was a rockslide two rocks hitting together could make a spark to ignite dry brush."

The fire is 80 percent contained, and crews don't expect full containment before Sept. 30. The far-off date is because the portion of the fire burning in Yosemite National Park is headed toward granite outcroppings that will act as a natural firebreak but won't be classified as technical containment.

Letting geological formations help will allow firefighters to focus some efforts inside the fire's footprint. Snyder said they have begun to cut breaks and start backfires in an effort to save grazing land, wildlife habitat and historic buildings left over from early timber camps.

"We don't want the entire interior to be burned too," he said.

Officials said 111 structures, including 11 homes, have been destroyed. More than 4,300 firefighters are still battling the blaze.

Although no cause has been announced, one local fire chief speculated the fire might have ignited in an illegal marijuana grow. His remarks posted on YouTube prompted Snyder to shoot down the rumor.