From either east or west, gain the Ashley Creek divide between Ashley and Post Creeks. Either approach involves a good deal of bushwhacking and off-trail travel. Like most climbs in the Missions, the approach is the crux of the climb. Giving a precise description of the approach thrash is impossible, and finding your own way is what being in the Missions is all about. Enjoy!
The eastern approach, via Island and Cliff Lakes, is a walk in park as far as Heart Lake, which is the end of the officially maintained trail. From there, a trail does go over Post Creek Saddle at the head of the drainage and down to Cliff, but it is exceedingly hard to follow between Heart and Island owing to large amounts of brush and downfall. Upon reaching Island Lake, the trail becomes somewhat more visible as it winds around the north shore and climbs over the divide.
The next tricky bit of navigation is around Cliff Lake, which is big and irregularly-shaped with many bays and inlets. Fording the outlet stream is the most dangerous aspect of the entire ascent, as it is deep, icy cold, fast-moving, and funnels immediately into a roaring chasm that drops into Disappointment Lake. This probably won't be a problem late in the season, but it is a great argument against taking this approach during the height of the snowmelt.
Reaching Icefloe Lake and the Ashley Creek Divide from Cliff is a matter of heading directly toward the peak, then turning south along the base of the prominent black cliffs that guard the lower reaches of McDonald's east face. Eventually you encounter the major stream that drains Icefloe and the small lakes below it.
From the Ashley Creek Divide, head straight up toward the summit. Before the July 15 closure, this will be mostly (or entirely) on snow. Much of the steep snowfield can be avoided by traversing left (see photo) and scrambling up the rounded buttress of scree and broken cliffs, but you will more than certainly (before July 15) encounter some moderate snow just below the top. McDonald has two main summits, with the westernmost (the one plainly visible from the Ashley Divide) being the highest. The ridge between the two is exceedingly narrow and heavily corniced in early season.
An ice axe is a necessity, and crampons would be helpful as well. A rope should not be necessary, as the south side snowfield's run-out is fairly forgiving if you stick to the direct line.
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