I'm wondering if what you have here is Pennisetum setaceum 'Rubrum' or another one of the red "fountain" type grasses? These grow all over California and can become huge clumps and 8' tall. Here's a link to some images in the PDB of Pennisetum setaceum 'Rubrum' http://plantsdatabase.com/go/1491/
I planted Japanese Blood Grass 'Rubra' four years ago and have been pulling it out for about 3 1/2 years. It can be very invasive and I'm still finding stragglers. Just went out and managed to find some pieces under some Jades at the back of our pond. They are greener than normal since they were "hiding out", but you can see the burgandy coloring and the margins that show some color. It only gets about 16" tall at the tallest here in 9b and runs along underground which makes it difficult to eradicate once established. I've never seen it with plumes, but then I've been digging it out before it could get to that stage. :-)
This plant is new to me, planted this spring 2003. I will watch for invasiveness -- thank you for the correction as to genus and for the warning! I know precious little about ornamental grasses save that they make a good archetectural statement in flower beds. One does not want too many of those, however...
Under Imperata someone says that there is a non-seeding type. I hope that's what I have, as it is too late to prevent any seed drop.