Photo by Chuck Kirman / Star staff Piru May 16, 2008: Firefighters spray water on hot spots in Holser Canyon near Lake Piru. The brushfire burned about 20 acres and should be fully contained early this evening.

Chuck Kirman / Star staff Firefighters spray water on hot spots in Holser Canyon near Lake Piru on Friday. The cause of the fire was believed to be accidental and related to gunfire at Piru Rifle Range.

Firefighters on Friday gained the upper hand on a brush fire that officials said was sparked by gunshots at the Piru Rifle Range near the eastern edge of Ventura County. Fire officials said they expected to have the blaze fully contained during the night.

The cause of the fire was accidental and shooting related, said Bill Nash, a spokesman for the Ventura County Fire Department. The blaze was ignited by shooters on the range at 6700 Holser Canyon Road.

"The range was operating within regulations and will be working with the Ventura County Fire Prevention Bureau to prevent future accidents," Nash said.

By late afternoon, firefighters had cut containment lines around 60 percent of the blaze between Piru and Lake Piru, Nash said. The fire had burned about 35 acres by late Friday, and some flames were still burning on its south flank.

No structures were threatened, and no injuries were reported.

"We're out ahead of it," Nash said. "We've made a nice advance on containment, and we got a break on the weather, too."

The fire was reported at 12:22 p.m. off Holser Canyon Road. Pushed toward Piru Canyon Road by 10 mph winds, the fire had grown to 20 acres by 2:20 p.m. The winds later shifted, slowing the fire's advance, Nash said.

More than 100 firefighters and support staff from the Ventura County, Santa Paula and Santa Barbara County fire departments, the California Department of Forestry and Fire Service and the U.S. Forest Service rushed to the scene. Water drops from helicopters and air tankers assisted with the firefighting effort.

"With the forecasts that we had for hot weather this weekend, we beefed up staffing levels, and when the fire broke out, we were able to respond with a full attack on it," Nash said.

The same site was scorched by last year's Ranch fire. Fed by early winter rains, light grasses grew back in the burned area. Those grasses burn quickly, but such fires are easier to combat than those in heavier brush, Nash said.

Firefighters planned to work through Friday night to extinguish the fire. Officials expect to be well into the mop-up stage by this morning, Nash said.

A smaller grass fire broke out Friday afternoon south of Highway 118 in Simi Valley but was quickly extinguished.

Friday was predicted to be the hottest day of the first heat wave of the season. Hot and dry conditions, however, were expected to continue today, with temperatures as high as 104 in local valleys, the National Weather Service reported.

Temperatures around 100 degrees were expected to continue in the hottest parts of the county Sunday before declining to the mid- to lower 90s next week. Highs in the 70s are expected at beaches through next week. No wind is predicted for the weekend.

Low humidity is expected, but not as low as during the catastrophic 2007 fire season, Nash said.

"We have concerns, but what we're not seeing right now are the conditions that have led to some of the firestorms we've experienced," he said.

Firefighters were battling a number of other blazes in Southern California.

A 35-acre fire broke out shortly before 11 a.m. in rolling hill country near Pomona in eastern Los Angeles County and burned within feet of some houses, said county fire Inspector Sam Padilla. But ground crews aided by water-dropping helicopters made good progress, and only smoldering hot spots remained by midafternoon.

In Riverside County, a blaze in Corona was expected to be contained at 5 acres, said Massiel Ladron De Guevara, spokesperson for the California Department of Forestry and Fire Protection.

San Diego County firefighters contained a small brush fire near Ramona and were fighting brush fires of a few acres each near Valley Center and Poway. No homes were threatened, and no injuries were reported.

Firefighters in San Bernardino County battled flames spreading through dry grass in the Chino Hills area, but no homes were threatened.

— The Associated Press contributed to this report.