At around 7:00pm 4-17-09 I looked out the kitchen window (its a western view) and saw what i thought was a cloud in a strange shape. So I went outside to look at it. I had a very clear view of the horizon and sunset What I saw was white and grey in color it was some sort of contrails miles long and very thick twisted into a distinct shape of a double helix and was stayin in the twisted shape and not disapating. There was no sign of what made it. It lasted about a hour before it moved out of sight. A week before this at 8:00pm we hear several sonic booms.