Vehicle’s hot part blamed in fire

The wildfire that forced the closure of Yosemite Valley this summer began when a hot part of a vehicle ignited dry vegetation along a key canyon highway route into the national park, officials investigating the Ferguson fire have concluded.

The U.S. Forest Service said superheated pieces of a catalytic converter — a piece of equipment on the belly of vehicles through which hot gases flow — are believed to have ignited roadside vegetation on Highway 140, along the Merced River. The roadway is one of just a few that bring motorists from the cities of California to Yosemite National Park.

The fire — which grew to nearly 97,000 acres, an area triple the size of San Francisco — was believed to have begun on eastbound Highway 140 the evening of July 13.

The area is an extremely vulnerable location — in the heart of mountainous wildland that had become a tinderbox. Many trees had been killed by five years of drought. Other trees were unhealthy and susceptible to infestation by bark beetles.

More than 129 million drought-stressed and beetle-ravaged trees have died across 7.7 million acres of California forest since 2010, mostly in the Sierra Nevada.

The dead trees left behind flammable needles — whether remaining on the tree, draping brush or carpeting the ground — the U.S. Forest Service has said, contributing significantly to the rapid spread of the fire.