Authorities say Elizabeth Schenk was visiting from the Bay Area when she went missing Tuesday morning.
The man who reported her missing told deputies Schenk had gone for a walk and had called him saying she was lost. He tried to provide her with directions but when she didn't return after a few hours he called authorities.
She is considered at risk due to her age and pre-existing medical conditions.
Authorities say Schenk was reportedly wearing a white sweater, white vest and white jeans when she left for her walk.
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Several agencies have joined the Mendocino County Sheriff's Office search for Schnek including California Highway Patrol, Westport Volunteer Fire Department, and CAL FIRE.
Anyone with information regarding Schenk's whereabouts should call the Mendocino County Sheriff's Office Dispatch Center at 707-463-4086.