Twenty years ago, while hiking the eastern segment of the Tonto Trail within the Grand Canyon, I found a 1900-s Barber quarter in nearly mint condition, about 40 yards south of where the trail crosses the drainage of a side-canyon named Grapevine. That point was more than 2 miles from the closest part of the South Rim (as the crow flies; several days away by foot), so it is unlikely that it was tossed from there into the Canyon. The up-facing side had a golden patina that blended fairly well with the surrounding talus stones. The underside was silver colored.
Given the superb condition of the coin, its date (1900), and where it was minted (San Francisco), my guess is that it was carried into the Canyon by one of a tiny number of hikers within the Canyon during the first few years of the 20th century (perhaps Emery or Ellsworth Kolb), and accidentally lost. Twenty-five cents was a lot of money to lose.
The coin is now on display at the Grand Canyon National Park Service Museum.
Bob