I've been through what is locally known as "Catherine Col" (not sure if maybe the same as "Glacier Pass") a few times.
Pretty straight forward from 1000 Is. up to the col, mostly slick rock and meadow. Some talus up top. It can be tricky dropping down into the N. Fk. It's steep and you can get cliffed out. You can avoid this by trending up canyon toward Twin Is Lake as you descend.
From Twin Island I have only been down the N Fk once. I remember it being slightly tricky as well until you hit the trail well below the lake. We may have missed it.
I've never been to Isberg from the lower NF drainage, but from the upper via Blue Canyon as well as the Lyell Fk of the Merced; spectacular country.
You can PM me if you would like more info.
Walk the Sky: Following the John Muir Trail
--- In firstname.lastname@example.org, "kneecreak" <kneecreak@...> wrote:
> We're thinking of a hike next summer from Thousand Island Lake over Glacier Pass then cross country across the N Fork of the San Joaquin, moving south to pick up the trail over Isberg Pass and into Yosemite. Is anyone familiar with the conditions and route finding challenges on the xc portion? Using the shuttle from Yosemite to Mammoth, this has the potential for an interesting non-supported trip.