@Heffa, also, these pictures were taken farther south than the the 215. This is near Durango and Pebble, so from this perspective it looks like the top of the mountain (because from this angle, you can't see the taller mountains behind it).
When I saw this last year, I was inside the Caesars Entertainment building on the third floor. From that perspective, it looks like it's IN (instead of on top of) the mountain, because from there, you can see the taller mountains behind it. Likewise, if you're traveling west on the 215, you'll see the taller mountains in the background, and this bright object would appear to be in the middle of the mountains.
I thought about this when I was driving home from work on the 215, looking at the same spot where the object was in the pic I posted, but viewing that spot from a location further north, i.e., the 215.
I took @Havasu's advice and looked on Google maps and see what looks like vehicles up there, so it's probably a mining operation taking place.