Good, fun, easy alpine route. Ian's guidebook gives great information for this route, so I won't belabor the point. I will say that once you are on route, stop looking at the guidebook or topo. Just stay on the ridge following the line of least resistance. Experienced alpinists will enjoy this route as a solo. This route has a lot of loose rocks on it. Be careful climbing under other parties. A planned trundle-party where no one is underneath the route would make this route a lot better. The rock quality is okay, never really more than that.
See the Poster Peak page and Ian's guidebook for approach details. Once up under Poster Peak at treeline, look for the buttress with the large obvious roof. Traverse around the left (SE) side of the buttress and look for the easy ledges that give access to the ridge.
Descent: Walk SE off the summit to the col along the SE ridge at 7130'. Hike down the loose gully back to the base of the buttresses. Catch the cairns back to the Haripin.
Experienced alpinists will get by with a single rack, a few runners. For those more new to the game and if you'd like to have more options when you run out of rope and are on a ledge with only one crack to work with, you may want a double rack up to #3, 6-7 runners. A double-length runner or two comes in handy when trying to reduce rope-drag on long leads through all the various ledges.