Martha Anne Overholser, 66, from Sault Ste. Marie, Mich., has been reported missing in Grand Canyon National Park in Arizona.
Information released by the park says Overholser did not return on a commercial bus tour.
The National Park Service is actively searching for her and reports she was last seen at the park on Dec. 10.
She was seen at Mather Point on the South Rim and is believed to have walked west from the Mather Point area, possibly towards the Bright Angel Lodge or Hermits Rest.