yes, afg, that's the description of yucca.
they have tap roots and the root can go pretty deep (not quite to china tho!
). they can be hard to get rid of because they will continue to grow from a piece of the root that is left when you dig them up...sounds like you didn't go deep enough with the backhoe.
swapguy, they propogate through the pups (you could also probably do seeds
too). you can either thin the pups out or leave them - your choice! just remember, where ever you plant
them, if you want to get rid of them later, it will be very difficult due to that tap root.