Shortly after the release of the song, in 1928, some local residents jokingly placed a sign at the base of a mountain, proclaiming it Big Rock Candy Mountain. The name stuck, and Big Rock Candy Mountain became one of the most recognized geological sites in Central Utah.
So, where DO those colors come from? From many millions of years of mineralization, caused by a complex chemical process involving hydrogen sulfide, steam, ground water, and oxygen.
About 22-35 million years ago, volcanoes in the area erupted, leaving a lot of lava and ash (Bullion Canyon Volcanics). The volcanic rocks are over 3,000 feet thick.
Iron minerals like jarosite, hematite and pyrite cause the yellow, red, and orange colors; potassium rich minerals like alunite and kaolinite cause the white color.
D&RGW Railroad used to provide service to this area, the Marysvale Line. It has been closed for a long, long time, but at the time it operated, it was an important part of the economy for this area: providing jobs, and hauling gold and ore from the many mines in the area.
The Eagle Rock Tunnel was part of this line, it was completed in 1896 and is 200 feet long, curving to accommodate the Sevier River on the South End. You can still access this tunnel from the Candy Mountain Express Bike Trail, or, if you don't want to ride bikes, you can pull off Highway 89 close to mile marker 187, and take a short hike across the Bike Trail.
The opening to the tunnel is fenced off, but you can get a good look inside from the gate.