Clinkers are what is left over when coal is burned. This is usually made up of the ash and other stone powders, or stones that might have been in the coal as it was burned. The name comes from the sound it makes as it strikes each other. They clink.
In Nature we see fires that break out in coal seams. Sometimes it is caused my man, other times it is from a forest fire, lightning strikes, or another ignition source that starts into the coal seam from the surface. Coal can also "spontaneously combust" with the right combination of moisture and oxygen it has the ability to start burning on its own.
Once burning most of the coal will turn to ash, and much of the material will go away, as much as 90% will vanish in the combustion. In a coal mine they are careful to make cuts (a tunnel) and leave large pillars standing. This lets the weight of the mountain rest on those pillars. However when coal burns underground it will nearly all burn, leaving large cavities with nothing to support the weight, also that heating/cooling changes the makeup of the rocks. So the rocks begin to collapse upon the void left behind when the coal seam burns.
When you look at the outcrops on the hillside to the right you see an example o the collapse, melting, baking, and twisting of the rocks from the heat of the coal burning.
Rock that is Green burns/melts without much oxygen nearby. The rock that is red is highly oxidized from the iron it it and the burning.
Look at the large stone by the road (if they happen to bulldoze that away at some point you can look about 40 feet farther east.
1-What colors are in the stone before you?
2-Is it one solid color? or a makeup of different colors? More oxygen or less used when this stone out-cropping was burned?
3-Does it appear to be baked? or Melted? Why do you say that?
4-Do you see any coal remaining in it?
5-Are there many gas cavities in these stones? Or do they appear to be solid?
Information from the Utah State Department of Natural Resources Magazine Geosights, Survey Notes, v. 39 no. 3, September 2007