It looks like what we call a "Centry plant" here on the s/e coast but I'm not sure. I have something that looks just like it that is Variegated and grows to about 5' in dia but it was given by a neighbor and I don't know what it's called.
Janet, it does look a lot like Agave montana, but your second source says the Agave montana does not have offshoots. Mine has lots and started making them when it was quite small.
The fact that it does produce offshoots, and it resembles Agave montana, could indicate it is a cross with another species but nothing is certain given the many species of Agave and and crosses which may have been made.
SORRY..in a mood right now 
