Very common in Sonoma county, everywhere it's damp. I've seen it clog drainage ditches, for example.
Met a man selling a natural beverage made from some sort of small tubers harvested from far eastern paddy-plantations of these or a very similar appearing plant. He had a pitcher of the stuff, it looked like the sweet rice drink that you can find in the better mexican restaurants.
If you think this observation is inaccurate, please add an ID, participate in the quality assessment above, or describe the inaccuracy in a comment.