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if you've corruption it either means you've missing symbols or symbols that overwrite eachother.
in direwolf's latest spotlight on mystcraft he explains pretty well how to write a stable age, because even the order of the symbols decide how an age will end up.
Be advised, a flat Extreme Hills biome is going to have ground level at approx 180. If you're planning a quarry age (as I did), be prepared for a LOT of dirt and cobble before you get to anything useful.
Do Extreme hills edge + extreme hills flat age
That should lower the height quite a bit.
Or just do a flat extreme hills edge, that gives the same resources.
Alternatively, you can manually dig down to 64 (or whatever) and start your quarry underground. Just be prepared for the monster spawner you just created