Fluff Piece

One of my favorite paths at Hahamongna Watershed Park is currently a winter wonderland. I'm pretty certain this plant is native to California. At this time of year it fills the area surrounding it in the Arroyo Seco with white fuzz. It's on the ground and in the branches. We're probably all breathing it right now. Sure is pretty, though.

You have to blow this picture up to get the full impact. I wanted you to see this the way I saw it, so I didn't adjust the colors or contrast. To give you some scale, the log at the lower right is about two feet long.

I searched the web but I don't think I used the right terms. Can anyone tell me what plant makes this white fluff?

Update, 7/11/09: Ann Erdman, aka Pasadena PIO, went to the trouble to email a couple of experts about this flora and sent me her results.
From Darya Barar, Certified Arborist at the City of Pasadena:
"The tree in the picture looks like an Arroyo Willow to me. I believe the maintenance policy in the arroyo is to allow trees to be as natural as possible.... that means in the fall there is no intervention by City crews."
and from Elise Jackson, Arroyo Seco Program Coordinator:
"Darya is correct. This is a native willow, a predominant tree in the Hahamongna flood basin, behind Devil's gate dam. The white 'fluff' contains the seeds which aids in the wind dispersal of these seeds. You can see in the photo the seeds (dark spots) mixed in the fluff. These trees definitely give Hahamongna the look of a winter wonderland, when the wind blows the white fluff completely covers the air and the ground, distributing seeds for the natural regeneration of our native willow woodland and providing important wildlife habitat."

Thanks to Darya and Elise for responding to Ann, and thanks to Ann for pursuing this information!