I bicycled the GVG from north of Nunda (which is pronounced Nun-day, by the way) where there is a dead-end at a washout down to the far side of Cuba (and on to my hotel in Olean) ten days ago. Quoting from my trip report (http://blog.russnelson.com/bicycling/1406977893.html" onclick="window.open(this.href);return false;):
Nunda to Olean, NY, riding the Genesee Valley Greenway. Very long ride, very rural rail-trail. Probably less rural than the GVG north of Nunda. Apart from Mt. Morris, there are no on-line communities in that direction. In this direction you have Nunda, Portageville (there's a convenience store at the top of the hill), Fillmore has two taverns that serve food plus a convenience store, Houghton is a college town with a supermarket and a Subway, Belfast has at least one convenience store, and then Cuba.
And the southern section differs from the northern section in being split up. North of Mt. Morris the trail is contiguous (or was, the last time I rode it). South of it, the trail has multiple closures, some seemingly for legal reasons, others because of unrepaired washouts, and others because of missing bridges.
I started my ride by heading up to the north end of the nearby section of trail. It dead-ends at a washout caused by a creek. Riding south from there, there is a fenced-off section between Creek Road and Pentagass Road. Then it picks up and continues to the point where the canal (which has left us) rejoins. It goes into Letchworth Gorge State Park and becomes Letchworth Gorge Trail #7. It curves around, hugging the wall of the gorge until it gets to a portion that has been washed out. There, you have to walk on a hiking trail. It seems like a long distance, but is only half a kilometer.
We're then back on the the GVG, soon to pass underneath the Erie's Portageville Bridge. Then we get to a missing bridge, and exit the railbed for the highway. A couple of blocks through town and we're back on the trail again. This runs to Bailey Road, where they built a bridge with no accommodation for the trail. You can leave the trail to go underneath the bridge, then ride along River Road to the next trail access crossing.
Another 4km of trail and you've gotten to the biggest and baddest washout, where the Genesee River has totally destroyed the railbed by meandering through it. There's nothing until Cemetery Road on the south side of Fillmore. A bridge over a creek is missing, but south of Cemetery Road the trail picks up again for 2km.
You can stay on the rail-trail all the way through Houghton until a missing bridge after the south of town. Then when the trail crosses to the west side of NY-19, it's open again until Caneada where there's a bridge out. The trail picks up again on the east side of NY-19. It crosses NY-19 just after the trail goes over an old highway bridge. It's all trail from there through Oramel to Gleason Hill Road south of Belfast.
Unfortunately, the trail is washed out south of Belfast all the way to Baragon Hill Road in Belfast. There you can pick up the trail for 5km until the village of Black Creek, where you're off the trail on side streets to Cuba, where there is a 1.5 mile stretch recently opened.
The parts that are on trail are pretty and mostly shaded. Some of the off-trail portions are busy roads or hilly roads, alas. Still, I enjoyed riding the GVG. There is now no portion of it that can be ridden that I haven't ridden.