The Black Crack is located at Cathedral Ledge in North Conway, New Hampshire. The following was taken from "Rock Climbs in the White Mountains of New Hampshire" (2nd edition) by Ed Webster. It is the essential rock climbers guide to the White Mountains and was very well done. "The closest version of a Yosemite -style off width on the east coast" Very true. Having climbed off widths there it was very reminiscent of such. The first ascent was by Mike Stultz, George Eypper and Joe Cote in July 1970.
The location is just inset right of "the arete"
The Black Crack is located on the upper left wall and can be gained by climbing any one of a number of routes on the lower left wall. Funhouse, Pooh and Orc may be good warm-ups easy enough to save the energy for The Black Crack. It may be best to just hike down to the ledge from the top. Looking at the face it may be gained by walking down from the left over by Nutcracker. Then traverse the obvious belay ledge that separates the upper and lower tier of the left wall. Another option may be to rappel from any of the rap stations at the top of the upper left wall. Directions to Cathedral ledge are available at the informative Cathedral Ledge summitpost page
This route is seldom climbed and is rated R for the protection. It is a sustained 5.10+ (probably 5.10C). There is very little along the lines for a comfortable rest. You could hang from either the bolt or fixed peg if you must rest. The climb is extremely pumpy and very awkward. The foot placements are essential. foot stacking was used and opposed pressure.
The crack is offwidth in nature. It was really awkward in places and getting your knee stuck may happen quite easily. Friends were used as the primary trad pro. Also there is a very thin crack just to the right of the main offwidth that offers placement for #3-#5 stoppers. getting these pieces of pro in was challenging because it was difficult to reach out to this crack and stay on. The route is luckily only one pitch of about a hundred and fifty feet. Expect to come out with some scrapes on the inside and outside of your knees. Also the crack is subject to drainage and may be dirty. It does not dry quickly.
Light rack is best. 2-3 of each #4,#5,#6 friends and small stoppers. med slings are sufficient.
Rock Climbs In The White Mountains of New Hampshire by Ed Webster by Mountain Imagery publishers is a great resource. Cathedral Ledge page also has great info