Luminous orange craft moving steadily, west to east, before vanishingWe were camping in Snake Creek Valley, which is a backcountry area of Great Basin National Park. The sky was perfectly clear, and the sun had recently set, so I believe it was around 9 pm. Earlier in the day, we'd travelled northward on US93 from the Valley of Fire, to the east of the test site, and on three occasions, we'd seen odd silver disks (one disk on each occasion) which appeared and disappeared (in fact, the sun was shining brightly and it was hard to follow them because they kept disappearing). We'd assumed that they were something out of the test site and in the campsite, we were joking about them when my friend looked up and called my attention to an oval-shaped orange light which moved silently across the sky from east to west at a steady speed, about twice as fast as a 747 would have appeared to move if it were flying at 35,000 feet; it also appeared to be at least four times larger than a 747 would have appeared at that altitude. The orange light was steady and not brilliant - much duller than a shooting star or a plane. After we watched it for about five seconds, it utterly vanished. It may be significant to note that we were about 17 miles southwest of the tiny town of Baker, but to the west, there were no towns at all before Ely, about 56 miles away.