They are there to prevent brush fires before they happen.
One of the volunteers, Joan Steiner, said she was spending Tuesday parked in her SUV, because she is concerned about the danger of fire in Orange County.
"We've had so many of them coming through this area," she said, "I have the time to do it, It's the least I can can do to help the community."
Rustic Santiago Canyon has been the scene of multiple wildfires, including one in October 2007 that destroyed a number of homes.
Steiner said the volunteers sign up for a post and act as a visible presence to deter would be fire-setters.
If they see suspicious activity, they report it. People who notice anything dangerous, such as someone flicking out a cigarette in fire-prone areas, can contact volunteers.
The volunteers then call authorities to follow-up.
Mostly, they are a presence to remind people -- especially in "red flag weather" -- about the fire dangers in the Irvine wildlands.