Nice site!

The closest one to what I saw is the Mt. Ranier one by Ed Book (the sixth image from the top). However, what I saw was:

-not nearly as large (it only took up about 20% of my field of view)
-much better defined
-appeared in an otherwise cloudless part of the sky
-appeared well above the rock formation, rather than around it
-was proportioned more like a bicycle tire than a doughnut