Does anybody? I’ve Googled all over the place and found some vague references, but nothing specific or trip reports, etc. Can anybody point me in the right direction (or clue me in as to why I should forget the idea)?
If you are referring to the White Mts. of NH you might want to check with the Appalachian Mt. Club, AMC. The AMC has been managing the trails and Hut system for something like 100 years along with putting out the trial system hiking guide book.
http://www.outdoors.org/recreation/
I have been hiking in the Whites since I was a kid in the 60s and have been on just about every trial and mountain and don’t recall sharing a trail with those on horses. I do remember seeing signage for bridal paths but it maybe very limited.
If you do find out where you can take a horse feel to get on to me and let know the areas. I know the whole range like my own back yard and can give you some insight on what to expect and the best bang for the effort.
If you are ever in Wyoming look into the Wind River Range. I have only done some climbing there but they do allow horses. But that maybe limited to permitted outfitters who pack in supplies for climbers and fishing camps. If not I think it would make for some spectacular trail riding.
You can check these guys ohttp://farmbytheriver.com/horseback-riding/ut - 
All the trails I know of are too steep/rocky for me to enjoy them from a horse. Those trails that do have good footing and appropriate grades are often very crowded with people.
Go look on the Equinesite.com bulletin board, though; there are a lot of New England folks there and a month or two ago, someone was asking about interest in overnight rides from their property. They said they knew of private trails that were suitable for horses. I think you can search for “White Mountains;” if you can’t find the thread, let me know and I’ll track it down.
I would love it if the xc areas like Jackson, Great Glen, Bear Notch, and Mt. Washington Hotel would open their trails for horses for, say, the last two weeks of October and the first two weeks of November, so after the busiest of foliage season but before things really get icy, but I don’t know how they’d feel about that.
Although I personally haven’t ridden in the White Mtns of NH, I know many of the hiking trails are steep, rocky, and quite technical. Some trails are even difficult for dogs, never mind horses. But there are a few old roads that aren’t traveled by cars anymore that people ride on, and I believe there is also a rail trail. Also, this property http://www.nhstateparks.org/explore/state-parks/connecticut-lakes-headwaters-working-forest.aspx recently added or is soon going to add a short (10 miles?) equestrian trail to see how much use it gets. If it gets used and they get support from local riders, they said they would add more mileage.
For more info on places to ride, ask your question on this facebook group:
https://www.facebook.com/groups/205029482868727/
A great group of riders, quick to share info and to show others new trails.
