Despite its simplicity this kanji is shafting me. I can't make up a solid story...

You might want to look at wikipedia and check out the history of charcoal making. I made a story that fits nicely with it.

http://en.wikipedia.org/wiki/Charcoal

Aint charcoal as black as ashes? It is just that it is mined from bellow the mountains.

Burning charcoal leaves a mountain of ashes? I never actually had a problem with this kanji - don't think I've ever failed it.

You will often see this compound in the newspapers: 練炭自殺... れんたんじさつ... (rentanjisatsu)... suicide by means of carbon monoxide poisoning. So.... maybe you can use this to help you remember? Burning charcoal under a mountain cliff is one way to commit suicide.