Okay. Here goes.
Wild trout have adipose fins. That is correct. MOST stocked trout have adipose fins as well. It is much to cost prohibitive to clip stocker trout, so the vast majority are not fin-clipped. The ones that are clipped tend to be trout in rivers that already have a wild, naturally reproducing population of trout in the system (or steelhead or salmon). Almost all trout that get planted into lakes are not clipped. Again, it would cost the state too much money to clip them.
The first few weeks after a hatchery trout is planted in a water way they will have a soft, white meat. This is due to the habitat (texture) and diet (color). After they've been in the river or lake system for a month or so their flesh will be as firm and as colored as any wild trout in the area, as they are feeding on the same foods and as active as their wild counterparts.
Brandon is correct that most lakes in the area do not have naturally occurring wild trout, while most rivers and streams will. Along this vein, most hatchery trout are planted into lakes, and many lakes now do have reproducing populations due to stockings years ago.
If you look at pages 72 and 73 of the report you linked to, there were 1,524,429 rainbow trout released in the Willamette zone in 2011 and only 59,458 brook trout and 43,774 cutthroat. That means based off of odds alone, if you caught a random hatchery fish I'm almost 94% sure it was a rainbow trout. For the Northwest zone 100% of trout released were rainbow. This makes it pretty safe to say that if you catch a cutthroat or a brook trout they are not hatchery. (I won't use wild with brook trout as they're non-native.)
To conclude I'll state my assumptions when fishing - if I catch an adipose fin-clipped fish in a river or stream odds are it's a juvenile hatchery salmon or steelhead. If I catch a trout with an intact adipose fin in a river or stream it's wild - and likely a juvenile wild salmon or steelhead (treat with respect). If I catch a rainbow trout in a lake (clipped or not) it's from a hatchery origin (either from reproducing hatchery fish, holdover, or fresh plant). If I catch a cutthroat in a lake it's wild. Brook and brown are naturally reproducing - but not technically wild.