Having just returned from 2 weeks in far northern Arizona and southern Utah, I don't doubt you saw condors in the Grand Canyon. We had a total of 11 condors in GC, starting with one soaring downstream at Marble Canyon which joined 9 more (!!!) at Navajo Bridge (also in Marble Canyon but specifically at the turnoff to Lee's Ferry), all of which were on the riverbank at the base of one of the bridge pilings, sunning themselves and "playing" with a piece of cardboard (Tag #s: 6, 70, 50, 52, A3, 42, 74, 97, 26 and one that was tagless). And the next day when I was at the South Rim of the GC, one was soaring just below Verkamp's but I couldn't get a good enough angle to get the tag #.
I didn't see any condors at Zion during the day I was there. Where exactly in the canyon was yours sighted?
FWIW, a Peregrine Fund person was at Navajo Bridge with a radio antenna tracking the birds, and he told me that #42 is a wild-hatched and -fledged bird in its 2nd year, so depending on whether you saw that particular bird and whether you're into ticking "only wild birds," it would seem that this one might be eligible for "listing." I personally don't list, but I was totally blown away by my first sighting of this huge bird -- the first one so close to the cliff edge I couldn't get both wingtips in my 10x42 bins! Yowza!
I don't know the exact point of release (and I assume there are several), but the Vermillion Cliffs is just "around the corner" from Marble Canyon and is one of the prime release points for the condors.