The cedar trees off Loop 360 are doing more than causing allergies this holiday season.Every morning since Thanksgiving more and more keep turning up decorated. It has become a quirky annual tradition in Austin over the last decade and very much a mystery of who is doing it and why.

It starts out as just as sparkle in the sunlight, but as drivers keep heading down Loop 360 near Spicewood Springs that sparkle soon gives way to this more than 100 cedar trees all gusted up and decorated like Christmas trees.

It's really nice to see when you are driving by during the day, passerby Larry Payne said.

I think it's pretty. No other city does it, driver Nicole McDaniel said.

I didn't expect to see so many, Kevin Surbaugh said. I just thought it would be one.

It does not matter how small or large; any type of cedar seems to work.Some are decorated in a traditional Christmas style, while others have a more of an Austin flare with flamingos, bees, and of course advertisements.

The decorators are not taking this lightly. Many of them use real Christmas ornaments like tensile balls and even true candy canes.

Most of the trimming happens under the cover of darkness, so the mystery of who is decorating, and why, remains.

Some of those questions were close to being answered by the McDaniel family.They came out to decorate a large cedar in the back of the pack.Nicole started doing it 15 years ago.

I did it back then and moved back a year ago, and I wanted my son to start doing it, Nicole said.

She does not know who started it or why either, but believes it is now mostly done at night by families like hers who just want to help Austin get into the Christmas spirit.

One captivated driver, though, had different idea. I think we got elves. That is what I think, he said.

With more and more night elves decorating trees even further south along Loop 360, the residents hope the holiday cedars will one day light up the entire highway.

The cedar tree decorations disappear at the end of the holiday season just as quietly as they appear. Right after New Years the secret elves always seem to take it all down.