I'm going to describe Gardiner in a bit more detail, since most of us aren't as skilled as RoguePhotonic, as well as my experience with the remainder of the Gardiner Basin "Trail" (if this is better placed somewhere else just let me know and I'll move it).
Start out following the Charlotte Lake trail west beyond the outlet of Charlotte Lake. Here it's a very good trail, probably still maintained, for about a half a mile. After you pass what is obviously an NPS stock holding area (there's some barbed wire and a few Knaack job boxes), the trail deteriorates, but stays obvious enough. It runs through a lot of mindless ups and downs, but generally contours along the slope toward the small bench below Gardiner Pass. Here you'll find a few good campsites (the best is on the east side of the creek). After the campsites, the Gardiner Basin "trail" seems to die out - a few cairns are scattered around and occasional runs of old tread can be found - but I ended up just wandering up a dry drainage (not the one shown on the map, but an apparent tributary to the west) toward Gardiner pass. Follow this drainage up to the bottom of a huge avalanche chute. Skirt the tangle of dead trees on the west side and just head straight up the slope toward the low point in the ridge.

Once on top of Gardiner, I was looking over a cliff. The chute mentioned by Rogue look steep, loose, and slippery - lots of sand-over-rocks that makes a good grip impossible. I moved over to the east and uphill about 50 feet and found a cairn marking the 'real' crossing of Gardiner Pass. The OpenStreetMap tracing of Gardiner Basin "Trail" seems to be dead accurate here.

- The real crossing - cairn on rock on left side
To my surprise/delight, this led me to a very obvious set of switchbacks that made the descent of the north side trivial. While they were obviously neglected, they were well-built in their day and made this pass comparable to many poorly-maintained USFS trails. The trail stays pretty obvious down to the creek below, then reverts to its previous state: occasional cairns, a few scraps of tread, but generally you're on your own.

- The switchbacks run to the right, then the left. Not in the best shape, but quite a treat for a "cross county" pass.

- Looking back at the north side. The switchbacks run through the timber right next to the cliff, directly up to the apparent low point in the ridge, while the chute mentioned by Rogue runs down the cliff immediately adjacent to the timber.
There's a particular spot near 9800' where the OpenStreetMap tracing seems to change from a more accurate tracing to a rote copy of the USGS line, apparently drawn freehand back in the 60's. This becomes significant around the 9500' mark, where the trail can be found again switchbacking down the steep slope to Gardiner Creek below pretty far off the mapped route. Cross over a little moraine at a carined spot, then follow a few more cairns down to Gardiner Creek.

- map2.png (246.3 KiB) Viewed 361 times
At this point the cairns seem to want you to cross the drainage, but I could not pick up the cairns on the other side. I stomped straight up a very steep but stable slope away from Gardiner Creek, then turned right and ascended the drainage parallel to the creek. I did hunt around quite a bit for the broad switchback shown above my route, but found absolutely no sign of a trail - I am very sure that tracing is in error.
Following Gardiner Creek up it was more of the same - cairn here, cairn there, but basically you're on your own. I did not find any scraps of tread up here, but just generally followed the creek and found my own route.
Near the little wasp-waisted lake at 11,063', I decided to bail off the Gardiner Creek "trail" and make my own way up to the outlet of Gardiner by contouring along the SW shore of the lake and then ascending just south of the outlet of the main Gardiner Lake. This went well, and saved me a bit of mileage and climbing getting to the outlet of the main Gardiner Lake, the nominal end of the Gardiner Basin "Trail".
"It is a wholesome and necessary thing for us to turn again to the Earth, and in contemplation of her beauties to know wonder and humility"
- Rachel Carson