OOC Stuff:
Anyone doing any sort of fact checking will know that cave-ins do not actually crush rocks. In fact, they actually make the rock problem much worse. So, there was a LOT of trickery involved. I'm going to list it here, for anyone who happens to read my story and has a pit full of 50,000 stones. Everything listed here was done with Exponents fantastic For Every Tile tweak.
Trial 1: I filled the bottom of the quarry with magma. This actually didn't do anything, because for some reason magma dropped down will kill dwarves, but not melt stones. It also doesn't act as a flow, even going so far as to hover over open spaces. Curious!
Trial 2: I set the temperature of each tile to 12000 (the value that Magma has). This melted the stone, but nothing else. After an entire season, I had a quarry full of molten rock.
Trial 3: I filled the quarry with 5/7 Water, and made sure that it started to move. Then I transformed all the water in the quarry to magma. Ah ha! Magma started to flow and melt the rocks! But the rocks never vanished. Damn it.
Trial 4: I set the melting point of basalt, rhyolite, and microline to 0, then cried as DF locked up for a forty five minutes. When it was finished, EVERYTHING IN THE FORTRESS that wasn't a wall that was made of basalt, rhyolite, or microline had melted. Every cabinet, door, floodgate, earring, and stone. Also, they never vanished. They just turned into molton goo, and pissed EVERYONE off as all their shit got wrecked.
Trial 5: I set the melting AND boiling point of basalt, rhyolite, microline, and alunite to 10069, then re-did Trial 3. Ah ha, success! Almost all the stones vaporized, except for the ones that didn't, but that's okay. However, when I set the magma level to 0, no one would go into the quarry because it was still as hot as a thousand suns. Forever.
Trial 6: I did the exact same thing as Trial 5, except at the end I changed the liquid type in the quarry to water, and 1/7. All the water boiled away super-fast, and cooled the tiles down to a proper level.
Whew! So, anyone who wants to undertake this take, skip all the other steps and do what I did in Trial 6.