I had just pulled up to a spot near the summit of Mt. Wilson (~1/2 mile from the gates of Mt. Wilson Observatory) to do some stargazing/astrophotography. As soon as I stepped out of my vehicle, the object caught my eye to the East. I initially thought it was a meteor, but immediately noticed it was moving much more slowly, and at a noticeably lower altitude, than any meteor I had seen. It looked to be at the same altitude as most cruising aircraft (~30,000 ft.) but traveled about 80 degrees from East to North-North East in about 5 seconds. When the sighting started, the object was about 40 degrees above the horizon, almost directly East, and I was able to follow it, as it traveled in a straight line, until it disappeared over the horizon, to the North-North East. The object appeared to have a leading edge, either a circular arc, or an obtuse rounded delta shape, with the trailing edge obscured by the trail/exhaust. The object glowed a very soft white/gray, and looked about twice the size of a 747 at 30,000 ft (which would make it about 400 ft. across at estimated altitude). The object emitted a dimmer, white/gray, patterned trail about 3 degrees long, and 1/4 degree thick, that tapered and dissipated quickly as the object traveled. The trail appeared to emanate in an alternating fashion, from the left and right side of the object in rapid succession (about every 1/6th second), leaving a trail of a corresponding, alternating pattern, during the entire sighting. I could see no red or green navigation lights common to aircraft. After the sighting I stood, somewhat in shock, staring at the spot where the object disappeared over the horizon. I looked around the sky for a few minutes, hoping to maybe see something similar, but didn't. I resumed setting up my telescopes and beginning long exposures, as the timed exposures were taking place I watched the skies. Aircraft were passing overhead, in common fashion, taking about 30 to 45 seconds to cover the same perceived distance as the object seen earlier. Other aircraft could be seen in the landing patterns of LAX and Burbank airports, all looking nothing like the object seen. Satellites of different brightnesses and speeds could be seen till sunrise, all appearing nothing like the object. I observed about 15 meteors over the course of 3 hours, with the longest lasting taking less than 2 seconds to cover 90 degrees, none leaving trails like the object, or appearing so low. I've been an amateur astronomer for over 20 years, and have not seen anything similar to this before.