Unusually short vapor trail

7:00 am Aug 13th, 2011, 10 miles north of Leavenworth, WA, near Lake Wenatchee and Fish Lake.
While out for a morning bike ride to photo graph the meadow at our camp ground in order to capture the morning mist as it sat atop the grass.  It was lovely.
I noticed a short thick vapor trail moving slowly and low across the northwestern horizon.  As is slowly moved just above the tree line I tried to figure out if it was a plane or something else.
I began to go through the process of deduction in regards to if it was a plane, why was there a vapor trail and why did it not look like the typical trail a plane would leave, which is usually when their dumping fuel.
I had my camera out, an Olympus E510 with a 150mm lense.  I was able to snap off 3 shots before it moved out of view behind the tree line.  I attempted to enlarge the shot, but could only see a blur of what appeared to be a cylindrical shape and appeared silver in color.
Still not sure, but it just did not look like the typical passenger jet or any other type of jet, military or other.