Me and a friend went to the north fork of the merced river in california to go gold prospecting and were going to stay for a week, around sunset approximately 8 pm, i noticed a light coming down the canyon. i called my friend over to watch what was coming down the canyon towards us, right about when he got over to me, it came out from behind the trees and into our field of vision. it was a blindingly bright orb of light,but it didn't hurt your eyes to look at it. the object was fifty feet above us and about the same distance away from us. we stared to try and figure out what it was as we watched it move across the open area in front of us, it seemed to be following the river. we estimated the size of the object to be around 12 to 18 feet across,and even though it was blindingly bright it didn't seem to be shining light on anything else, then we moved over a bit so we like continue to watch it. my friend said he was scared, i was calm and told him i thought we would be ok since it was going downstream from us. we kept questioning each other what the other saw, trying to estimate how high it was, if we could see the light shine on anything, how fast it was going and if we could hear any noise coming from it. neither of us could hear it make any noise, we both thought it was going about 25 or 35 miles per hour, as it got down river it came close to a cliff face and we could see it light up the cliff some, but not brightly, it was in the canyon about fifty to one hundred feet off the ground. and definitely under intelligent control. it turned following the river and continued to travel at the same speed then turned again and went be hind a small hill, we could still see the glow of it as it went behind a second hill then we couldn't see it any more. my friend was quite upset about the whole experience, i calmed him down and after awhile we went to bed. the next morning my friend wanted to go home so we packed up and went.