I compared the list of trails we have listed on this site to the "official" list on the FS website, and came up with what appears to be several trails which the FS has abandoned (many of these were on the official list only a few years ago):
- Burnt Granite - this probably got abandoned (for the second time) after they decommissioned the "easy" road to it. Now it takes a long detour to get to the trailhead.
- Geronimo - this one is in danger of disappearing, especially since the fire a couple years ago. It was faint before and I'm sure the fire wasn't kind to it.
- Mt Lowe - this one probably sees a reasonable amount of traffic - it is a short trail to the old lookout site.
- Olallie Butte (this one is probably not in danger of disappearing - it gets a fair amount of use)
- Plaza Creek - this one gets VERY faint the closer you get to the Roaring River.
- Pyramid Butte - this one is really sad - the trail is in EXCELLENT condition to the site of the old lookout, and there are fantastic views from this site.
- Rho Creek - another really sad one - this trail was recovered by advocates several years ago, and even got new signage - it is a beautiful trail through several different types of forest - very unique.
- Top Lake (this one really surprised me)
This list really surprised me, especially Top Lake and Rho Creek. So, for all you anonymous trail advocates out there, please seek out some of these trails and help make sure they don't disappear. They are all interesting trails for different reasons and deserve to be preserved.
How sad the Forest Service chooses to just abandon perfectly good historical trails. 
Rho Creek, abandoned again...the FS JUST put that one back on the inventory a couple years ago! What the hell is this the 70s again? Is the Clackamas just a big plantation?
Burnt Granite needs serious brushing out etc. It is a worthy project, showing up on the 1897 map as a main route.
Plaza Creek, that one has been faint since the 50s...
Craziness. You can't even count on the roads being there, just berms everywhere.
I don't know for a fact that these trails are officially abandoned - I'm making an assumption that since they do not appear on the FS website, that they are no longer considered official trails. I think that is a reasonably accurate assumption, however.
Burnt Granite should be kept around - it is an interesting walk - and interesting up on top. Too bad the trail up to the old lookout spot is history - there is a LOT of blowdown up there. I bet it would take a week or more to clear all the blowdown up there.
Rho Ridge appears to be abbreviated too, only the southern half is shown:
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5405700.pdf
That is really sad. We did the whole Rho Ridge trail about 3 years ago and it was in good shape. I don't know why they want to abandon the northern section. The interesting part is that those FS data files showed the whole 10+ miles from Mt Lowe down to 6355.