The danger level for Angeles National Forest has been raised from high to very high, which is the fourth in a six-level, graduated fire danger rating system.
Two years ago, the Station Fire swept through the Angeles National Forest, destroying 250 square miles. Two firefighters died.
Since then, vegetation has started to grow back.
With high temperatures, low humidity and big crowds expected this weekend, officials are concerned about campfires. They said most forest fires are caused by humans.
"If they are going to have campfires, have those campfires in developed sites. Make sure they have some type of water or tools to put the fire out after they leave the camping areas," said Deputy Fire Chief James Hall of the U.S. Forest Service.
The San Bernardino National Forest is also warning of increased fire danger.
For both forests, permits are needed for any gas or propane-fueled stoves. People are asked to check spark arrestors on vehicles, always stay on designated roads and never park on dry brush or grass.
There also are some areas where wooden charcoal burning is prohibited. The Forest Service will be citing people who don't comply with the restrictions. That can include $10,000 in fines or six months in prison.