What's a good way to find magma in Dwarf Fortress v0.31.08 (or thereabouts)? (Preferably without cheating.) I know if I dig straight down I'll eventually find some, but I usually wind up breaking into an underground cave with unfriendly creatures and I'd like to avoid that. Also, I'd like it to be a little closer to the surface so I don't have to build some kind of insanely large pump stack to move the magma up to a useful level.
Should magma like this be available on most maps or is it highly dependent on embark location? Should I look 20 levels down and dig a grid? 40 levels?