Chee Tse, who was reported to be in the early stages of dementia, was found dead around 9:45 p.m. along a fence outside Cache Creek Casino on state Highway 16 in Brooks, Williams said.
Tse had last been seen leaving her residence at 1901 Larkin St. Tuesday morning.
Police said Thursday that she most likely took a tour bus around 8 a.m. from near Kearny and Clay streets in San Francisco to Cache Creek Casino in Brooks, Thunder Valley Casino in Lincoln or River Rock Casino in Alexander Valley.
Police put out calls to those locations and learned that she had been captured on camera walking out of a building at Cache Creek Casino Resort, Williams said.
The cause of her death remains under investigation and Williams said there were no obvious signs of trauma.