It was about 8 in the evening and a ranger was starting to close the gate at Lodi Lake's Nature Area.
Lodi Parks Director Steve Dutra says a family of three was making a quick exit but not before telling the ranger what they saw.
"They had seen a mountain lion on the property, said they took a picture of it, they left quickly so we didn't get names, phone number, or an opportunity to look at the picture," said Dutra.
The park was closed and Fish and Game officers were called in to search the area which Dutra says is home to many kinds of wildlife.
"It's well populated with deer, raccoons, possums, the No. 1 county migrating birding area so yes, lot of wildlife," said Dutra.
The park has been reopened after a search failed to find any evidence of the mountain lion, but signs have been posted as a precaution.