Two fires flanking Riverside County are still burning.

However, with some help from Mother Nature, firefighters continued making significant progress Monday in stopping flames before they reach the county line.

Both the Santiago fire to the west in Orange County and the Poomacha fire in North San Diego County were listed Monday as being 65 percent surrounded by firefighters.

Firefighters are working around the clock to get both blazes surrounded by the end of the week when a fresh set of Santa Ana conditions, possibly bringing gusty winds, could again hit the area.

Officials said Monday that the blaze in Orange County was, in some spots, less than a mile from the Riverside County line but still several miles from any populated areas. The Poomacha fire burning south of Aguanga was about three miles from entering Riverside County, fire officials said.

The arson-set Santiago fire had consumed 28,400 acres and is still burning in the Cleveland National Forest, while the Poomacha blaze has destroyed 49,540 acres and continues to threaten Palomar Mountain and the Agua Tibia wilderness, officials said Monday afternoon.

"Our No. 1 priority is to prevent this from getting into Riverside County," Angela Luedtke, a spokeswoman for the Orange County Fire Authority, said about the Santiago fire.

With cooler weather and an increase in humidity levels, fire crews were able to get a lot of much-needed work done on both fires Monday.

On the Santiago fire - a great concern to about 20,000 residents in the Temescal Valley area between Lake Elsinore and Corona - that progress meant more fire lines being bulldozed ahead of the path of the flames.

"A lot of dozer work has been able to be done," Luedtke said. "They have about six more miles of line left to cut."

Many water and fire retardant drops were also being done, she said. There were more than 1,700 firefighters, 12 helicopters, eight fixed-wing air tankers and 18 bulldozers assigned to battle the blaze Monday.

The closest point of the blaze from the Riverside County line was less than a mile, said Larry Tunforss, a Fire Authority information officer.

One of the goals of fire management teams "from the get-go," Tunforss said, was to not let the fire cross into Riverside County, where flames could take off and threaten those who live just a few miles from the county line.

Monday's weather was a "double-edged sword," according to Tunforss. While it was cooler and allowed firefighters to make some progress in better conditions than before, the winds picked up a bit, he said.

"So that moved the fire a little," he said.

There are new concerns with the forecast of higher winds possibly arriving by Friday or Saturday.

"We are trying to get this thing put to bed before that happens," Tunforss said.

While many firefighters assigned to the Santiago fire are still working to knock down any active flames and mop up previously burned areas to prevent flare-ups, there are still quite a few firefighters protecting numerous homes in the canyons.

The fire has destroyed 15 homes and damaged nine others. While there are some areas still under a mandatory evacuation, many residents have been allowed to go back home.

"They can go back home; they just might have to plan on cooking for more people to feed those hungry firefighters parked in their driveway," Tunforss said with a laugh.

Officials hope to have the Santiago fire 100 percent surrounded by Friday.

In North San Diego County, the Poomacha fire burning south of Aguanga is expected to be surrounded Wednesday and completely extinguished by Monday, officials said.

"We are currently working on top of the north end of Palomar Mountain and the Agua Tibia wilderness," said Audrey Hagen, an information officer with California Department of Forestry and Fire Protection, on Monday.

"It's not really moving at this time," Hagen said of the blaze.

Firefighters took advantage of milder weather conditions to set backfires Monday to burn areas ahead of any active flames, she said.

"Its just a matter of getting a line around it at this point," she said, adding that crews are also doing mop-up work inside the charred area to prevent flare-ups.

There are about 2,600 firefighters still assigned to the Poomacha fire, Hagen said.

- Contact staff writer John Hall at (951) 676-4315, Ext. 2628, or jhall@californian.com.