Fire retardant falls on burning area near Interstate 8 by Tavern Road. Photo by Chris Stone

Updated at 10 p.m. July 11, 2017

Automobile exhaust sparked a fast-moving wildfire that blackened about 400 open acres near Lake Jennings Tuesday, forcing evacuations of some back-country homes and prompting a full closure of a several-mile stretch of nearby Interstate 8, authorities reported.

Work crews clear brush on a hillside near Interstate 8. Photo by Chris Stone

The blaze erupted alongside the freeway near Olde Highway 80 in Flinn Springs shortly before 2 p.m., according to Cal Fire.

The flames soon were posing an immediate threat to five homes, the state agency reported.

Authorities directed those living along View Side Lane to clear out of the neighborhood while ground and airborne firefighters worked to corral the blaze.

County officials also issued an “evacuation advisory” for Peutz Valley and the northern end of Harbison Canyon in the Hunter Pass area, alerting residents of those locales that they might have to vacate if the blaze kept moving in their direction.

Temporary shelters for evacuees were established at Granite Hills High School on East Madison Avenue in El Cajon and at Joan MacQueen Middle School on Tavern Road in Alpine.

A photographer’s SUV had been in the pathway of the fire retardant drop off Interstate 8. Photo by Chris Stone

As the fire rapidly moved across hilly terrain to the southwest, the CHP shut down nearby Interstate 8 between Tavern and Lake Jennings Park roads. The closure resulted in hours of gridlock for miles to the east and west.

By 5 p.m., crews had halted the spread of the fire, allowing for the reopening of the westbound lanes of the interstate in the area.

Two eastbound lanes remained closed as of about 9:30 p.m., according to the California Highway Patrol.

Investigators determined that engine emissions from a passing vehicle ignited the blaze, which was 10 percent contained as of 9 p.m., according to Cal Fire.

— City News Service 

Chris Jennewein is founder and senior editor of Times of San Diego.