And those who respond to these sightings will need to think twice before they act. A new law goes into effect in January, aimed at protecting mountain lions that pose no immediate threat to people.
It all began a year ago when two mountain lion cubs were shot and killed by game wardens. It prompted a new law; a definite victory for animal rights advocates.
Wildlife advocates got together Sunday to remember a sad day one year ago, when two mountain lion cubs were shot and killed by game wardens after they wandered into a Half Moon Bay neighborhood, and hid under a porch.
"There were better ways of handling this, than with a gun," neighbor Richard Kirchner said.
"They were baby cubs," said Senator Jerry Hill, D-San Mateo. "They weren't posting a threat. They'd wandered into the neighborhood, they were looking for their mother, they were looking for food."
The killings of the cubs sparked so much public outrage it prompted Sen. Hill to push forward legislation requiring wardens to use non-lethal alternatives to capture big cats, unless they pose immediate threat to the public.
Hill's law takes effect next month, but is already being used by game wardens.
"And we've seen it work in San Jose, Santa Cruz, and Los Angeles where they've already relocated mountain lions that probably would've been killed otherwise," Sen. Hill said.
The law is allowing more collaboration with wildlife groups like the Mountain Lion Foundation.
"We lost the wolf, we lost the grizzly, but we still have mountain lions, we still live in a state that has lions," said Amy Rodrigues with the Mountain Lion Foundation. "And that's exciting, and there's a lot of people who feel the same way, and they really want to keep these cats around."
Mountain lion sightings are common in San Mateo County, and many people want to see more of them in the future. The new law has the support of California's Department of Fish and Wildlife.