This is a picture from the neighbor a few doors down. This Pampas Grass (Cortaderia jubata ) started off as 4 small plants but have quickly taken over this street-side area. I have noticed that this grass can be extremely invasive and I often see it cropping up in the wide variety of wild areas surrounding the San Fernando Valley. Worse still, we have a man-made wildlife reserve less than a mile away and I have seen large clumps of this grass popping up there as well.
The National Park Service has a page regarding the invasive nature of Pampas.
It seems the grass can create seed without pollination and it produces a large amount of seed that is easily distributed on the wind. I am a bit surprised that it isn't more widespread here, but assume that the dry climate helps to keep it in check somewhat.
While it can be very pretty in your garden, you might want to think twice about planting Pampas. It might take over your garden and those of your neighbors, as well.