Ive caught quite a few...but not by accident, i went out to bodies of water with populations of them and targeted them specifically...mostly in Rocky Mountain National Park. I usually try them in the summer and fall, by then most of the high country water is open and fishable. if you want some easier access to them try Lilly Lake in Estes Park...ive seen some pretty good sized ones there, although the lake gets lots of pressure and is kinda windy at times. In that lake i usually sight fish to cruisers with nymphs...ive had more luck with that tactic that with dries. (miracle nymphs and small Hare's Ears work well...as a dropper under a larger Griffith's Gnat) On the rivers ive done well with the usual summer time dry fly patterns....and especially terrestrials like hoppers and bee patterns. ive also had lots of luck with the good ol Royal Wulff...
they are definately a beautiful fish...worth the effort of a 5 mile hike if you are willing.
If you want to catch greenbacks I also suggest Rocky Mountain National Park. I recommend talking to Kirk Bien of Kirk's Mountain Adventures in Estes Park. He knows the park like the back of his hand and can give you some great info on where to catch some bigger cuts.
It's east to find green backs if you just do a little research. Also speaking of big ones, check out North Park Anglers sight. There is a pic of a huge one. Called them and all they would say is it came out of the park.
Easiest places to catch greenbacks is some of the lakes in RMNP - the fish are larger, but not necessarily genetically pure greenbacks. For years, slightly hybridized fish were stocked in various places before genetic testing discovered that some of the brood stocks weren't pure. The best places for pure greenbacks are secret and remote. They are as big as their environment can support - smaller in streams, bigger and more accessible in lakes. Please treat these fish nicely. They are the Colorado State Fish and so far their recovery has been a success. We may get them off the "Threatened" list, eventually. Here are some pure stream greenbacks:
subspecies, actually (oncorhynchus clarki stomias). One of four subspecies of cutthroat trout (Oncorhynchus clarki) native to Colorado - one of which has been extinct for the better part of a century (Yellowfin cutthroat), and was once native to Twin Lakes, where it reportedly reached very large sizes.
Try Spruce lake in RMNP. It's a 4-5 mike hike from Bear Lake but well worth it. Three of us went up there in the fall and caught about 75. They killed the dries. Mosquito,
adams, griffith, humphys. Not much room to backcast but roll cast was sufficient.