This is the easiest route on Iceberg Peak in technical difficulty, but it is exhausting. It can be done in a very long day from the Loop, but it is better done combined with an overnight stay at the backcountry campground or the chalet in Granite Park. The approach and the climb are both almost entirely above treeline, and views are excellent the entire way.
The route leaves the Highline Trail 3.5-4 miles north of Granite Park and ascends talus and/or snow slopes to reach the western side of the peak, where it is a steep talus hike to the top, although climbers will likely encounter Class 3 and perhaps even Class 4 conditions (without bad exposure, though) unless they happen to find the climber’s trail up there (it is easier to find when descending). RT distance from Granite Park is around 11 miles, with around 3000’ of elevation gain in all. You will leave the trail at about 6500’, leaving about 2650’ of elevation gain to go.
Park at Logan Pass on Going-to-the-Sun Road if you wish to approach via the Highline Trail (arrive early). Park at the Loop, which is about 9 miles west of Logan Pass, to use the Loop Trail. If the parking lot you wish to use is full, consider parking at one of the shuttle bus stops and using that system (free) to reach the trailhead.
To reach Granite Park, one must hike almost 8 miles along the Highline Trail from Logan Pass (but the hike is easy, with little significant elevation change) or hike the Loop Trail, a more strenuous trail that gains about 2500’ in elevation over 4 miles.
The first of the following paragraphs is a paraphrase of the route as described by J. Gordon Edwards in A Climber’s Guide to Glacier National Park. The second and third detail my personal experience with the route. Both accounts start from Granite Park.
After the Highline Trail turns sharply to the right and descends along the north wall of a large cliff to cross an extensive snowfield, leave the trail slightly north of the snowfield and head uphill. A sill of black igneous rock is the only obstacle, and an easy route through is apparent a bit further north. From above the sill, it is a long scree scramble up the west side of the peak to the summit.
Do not take the trail portion of this route lightly. In late summer, the trail will be mostly or entirely snow-free in most years, but earlier in the summer, there likely will be several snowbanks blocking the trail. When I covered this route in early July 2008, the trail was more than 50% snow-covered, and I needed my ice axe for safe passage in the early morning. Furthermore, about 3.5 miles from Ahern Pass, there was a wide, steep snowbank that was difficult and dangerous to cross (this is the snowfield Edwards says you cross and descend just before leaving the trail), especially since I had to descend it in order to regain the trail. I had to climb along the upper edge of the snow, using cliff edges for additional support, until I reached a section where the angle was more moderate. I know that snowbank had already turned back several hikers that summer, and I believe I was the first to cross it that summer. It can be inferred from the Edwards guide that this snowbank is present for most of the summer in most years, though it likely will be smaller and easier in drier years or later in the summer.
Once you enter the great basin after the steep snowbank, you just have to pick your path up. It is possible to stay off the snow, but if you have an ice axe, it is easier to climb the snow as much as possible rather than hiking up the talus. The black igneous sill (a low cliff band) that Edwards describes is obvious, and he is exactly right about trending north to find an easy way through. No matter how far off course you may think you are getting (you actually aren’t, as the summit actually is mostly north of you), keep climbing up and heading north until you see a good way through the cliffs. Hiking or easy scrambling is required; if you are facing something harder, keep looking for an easier way. Once you are above the sill, the way up is obvious, and the summit soon comes into view. You still have around 1000’ of climbing to go, but the views start expanding and make the trudge more bearable. You may find occasional cairns or even a climber’s trail, but if you don’t, it doesn’t matter. If you are careful or lucky, you will find the Class 2 trail through the summit blocks and cliffs and up to the top, but expect some Class 3 scrambling instead. If you face Class 4 or harder and don’t like it, step back and look for easier going.
Much of the rock in the summit area is quite rotten.
Descend the way you climbed or consider the South Iceberg route instead (that route is scenic and high and avoids the dangerous snowbank on the Highline Trail).
Because there is so much steep scree travel on this route, it is important that you have sturdy boots that offer good ankle support and whose soles can stand a beating. And because of the likelihood of snow on the trail and the climbing route, you should have an ice axe and perhaps crampons as well.