Cheesecutter, red elm is the "easy" elm to split. Siberian (already mentioned) and American elm are stringier yet.
I agree, Red Elm is usually no problem splitting... most of it is pretty straight grained and "pops" open much like Red Oak. Admittedly, the splitting gets a bit tougher when it gets dry and hard... ya' need just a bit more force to get the split started, but it still tends to "pop". Now, American Elm is another story... that stuff can cause an 8# maul to bounce like it was made of rubber, even when swung by the largest behemoth of a man. American Elm will also "prove" a hydraulic splitter... forcing the machine to "work" during the full length of the split (and still leave the two pieces attached solidly enough you can not pull them apart).
One time, and one time only, in my young, dumb and bullet proof past, I split a large American Elm using wedges, sledge and maul... just one time, never again... I made myself a promise to never do it again... and I never have. It is the soul reason I have a hydraulic splitter, without it I would ignore American Elm like I ignore the people who hug trees.
Where do you find it??? Well, at one time, before Dutch Elm Disease, the American Elm grew near everywhere from the Atlantic to the Rockies... but now, east of the Mississippi, they're near extinct, and the further east you go the rarer they are. West of the Mississippi there are still some hold-outs; I have a couple (live) in my woodlot I couldn't put my arms around if they were twice as long as they are now... but DED has been making another run at them the last couple years, I do believe I will see the end of the (wild, non-hybridized) American Elm in my lifetime.
