Rumors about who or what started two wildfires two days before a presidential visit to Central Oregon were as thick as the plumes of smoke billowing from the blazes.

Arsonists. Eco-terrorists. Angry loggers.

Accusations flew, both in private and in public. The timing of the fires, the presence of Secret Service helicopters and the national attention focused on the area prompted even some high-ranking agency officials to speculate on the fires’ causes.

”I have to admit that when it happened, I, like a lot of people, suspected arson,” said Bill Anthony, district ranger for the Sisters district of the Deschutes National Forest, where the majority of the Booth and the Bear Butte fires burned.

This week, though, many of those suspicions were put to rest. On Wednesday, the Central Oregon Arson Task Force announced that investigations into the two fires – which merged to become the 92,000-acre B and B Complex – showed that the blaze was sparked by lightning strikes two weeks before the flames erupted.

Some skeptics say that scenario is impossible. Joe Keating, projects director for the Oregon Wildlife Federation, said Friday it was ”ludicrous to suggest a fire could smolder in the bone-dry forest for two weeks without a major ignition.”

But investigators who spent the past two months searching for evidence, determining the location of where both fires started, interviewing witnesses and following a variety of tips stand by their conclusions.

A group of investigators released their findings at a public meeting this week at the Sisters Middle School. Here are some of the facts investigators uncovered.

An electrical storm moved through Central Oregon during the period of Aug. 4 through Aug. 7. Immediately following that storm a series of fires broke out, according to Bill Selby, smokejumper operations manager at the Redmond Air Center. His records show that smokejumpers attacked and extinguished 17 fire starts from Aug. 7 through Aug. 19.

Three of these fires that officials believe were caused by lightning broke out just before the Booth and Bear Butte fires. One erupted on Aug. 15 and two erupted on Aug. 18.

Smokejumpers were not able to jump the Bear Butte or the Booth fires on Aug. 19 because wind gusts of up to 40 miles per hour made the mission too dangerous.

In the days before the fires, there was helicopter traffic over the forest. Five helicopters associated with the upcoming presidential visit flew missions over the period of Aug. 17, 18, 20 and 21.

On the morning of Aug. 19 – the day the fires erupted – a pilot from the Oregon Army National Guard left Salem for Bend. His mission was to ferry Secret Service officers around that day.

On his trip to Bend, the pilot circled his chopper three times over Santiam Pass. He told investigators he hunts in that area and was looking for big game.

A Warm Springs firefighting crew spotted the Bear Butte Fire, located in the northern part of the forest near the Confederated Tribes of the Warm Springs reservation. It was sighted at 12:57 p.m.

Smokejumpers flying a reconnaissance flight spotted the Booth Fire, located about a half mile north of Highway 20 near the Square Lake Trail at 3:23 p.m.That was enough to get the teams started.

Both fires underwent individual investigations, said Randy Wright, a team member and investigator for the Deschutes County Sherrif’s Office.

The Bear Butte Fire, the more remote of the two, began in steep and rocky terrain. A rocky slope just east of where the fire began gave way to an upper elevation forest comprised of mountain hemlock, as well as several varieties of fir.

Three weeks after the fire erupted, investigators hiked into the point of ignition, said Bill Welch, a member of the arson task force.

Tracing the burn patterns on some of the trees, the team discovered two trees whose bark had been stripped, giving evidence of lighting strike, he said.

Officials believe one of the trees conducted the lightning strike to a neighboring tree. The electrical current from the lightning sparked a fire within the trunk. They believe there was enough material to get the fire to smolder, like hot coals on a barbecue.

After about two weeks, the smoldering mass had eaten through the tree’s trunk and forced the tree to fall on Aug. 19.

Once it fell, the tree exposed the flames to the windy atmosphere. Weather records show the temperature reached 85 degrees, wind speeds averaged between 6 to 12 miles per hour, with some gusts, and the relative humidity was about 22 percent.

In other words, the conditions were prime to start a wildfire. The Bear Butte Fire eventually grew to about 11,240 acres before merging with the Booth Fire.

That same day, about 10 miles southwest of the Bear Butte Fire and about two and a half hours later, the Booth Fire flared up.

Investigator Gary White said to better pinpoint the fire’s location his team interviewed four hikers who were camping in the area and saw the flames.

When they found what they believe was the point of origin, it was a ”moonscape,” he said. Save for several trees with grasses at their base and which bore severe lightning scars – virtually no bark was left – a blackened forest standing within charred and ashen soil dominated the landscape.

White said the remaining grasses indicated that was where the fire began.

”The fire is just starting there, and it is not burning so hot, so it leaves some of the finer fuels,” he said.

As in the Bear Butte fire, officials believe that lightning struck a tree and started a fire which smoldered within the tree’s trunk.

”All the burn indicators led us right back to the base of the tree,” he said. ”There was a creeping pattern in the duff (decaying matter on the forest floor) to a tree that burned through and fell over.”

Despite their confidence that lightning caused the fire, investigators do not know for certain that lightning caused the fire, White said. The team did not find any evidence of an explosive, but cannot categorically rule out arson, he said.

However, the area’s remoteness made it difficult to reach, he said. The forest backs up into a hill, practically cutting off any escape route.

”Someone would have about 30 minutes at a dead run to get down to the trail if they went up there and started that fire,” he said.

That left lightning the most probable cause of the fire, he said.

To environmentalist Keating, such reasoning raises major questions.

Keating of the Oregon Wildlife Federation, questioned the findings that a lightning-caused fire smoldered for nearly two weeks.

”I know that forest inside and out, and I know how bone dry it was,” he said.

Keating said he routinely hiked ”in the Three Sisters area.” He called upon Gov. Ted Kulongoski to convene an independent investigation into the findings because he thinks the investigators were biased.

But the governor will not investigate the cause of the fire further, spokeswoman Mary Ellen Glynn said on Friday.

According to lightning behaviorist Don Latham, the smoldering fire makes sense. A retired fire scientist, Latham built his career at the Fire Sciences Lab, an arm of the U.S. Department of Agriculture Rocky Mountain Research Station in Missoula, Mont., and distinguished himself within the scientific community for research on lightning.

”There is a difference between the ignition of a fire and whether a fire will spread,” Latham said from his Missoula home. ”There is no average time for smoldering. Smoldering happens if it is in a thick layer several inches deep, and they put out very very tiny amounts of smoke.”

For instance, fires may smolder within moss, tree trunks or deep layers of duff, he said.

”Unless you felt the warmth close to the surface, you wouldn’t know a fire was smoldering,” he said. ”You might sniff smoke, but you wouldn’t see it.”

Smoldering fires can travel at about 3 centimeters per hour, a ”very slow pace,” he said.

”They will keep burning until they hit conditions that are right,” he said. ”Then they jump to the surface, dry out, hit material and will burn from there.”The arson task force says the case is closed.

”Our investigation is not bullet proof,” said Ron Pugh, investigator with the Forest Service. ”We wish it were. But still, the evidence is pretty powerful (that lightning caused the fires). If there was any chance of arsonists, we would still be knocking down doors.”

Rachel Odell can be reached at 541-617-7811 or rodell@bendbulletin.com.