Most of the photographers I was around on this trip were haranguing against the jet trails. I didn't know I was supposed to dislike them and thought they created an excellent accent of light. I don't believe you can visit Yosemite and screen out the effect that humankind has had and is having on nature. I think many of us would like to erase the presence of people from the park and just focus on the natural beauty, yet people are an element of any trip to the Yosemite Valley. Sometimes they create ugliness and sometimes beauty. Here the diffusing jet trail creates a stunning background for the tree. Note: my friend Phil Douglis is not one of those haranguers, here is an image where he uses them also: http://www.pbase.com/pnd1/image/35602348