Beginning from the busy Glen Alps trailhead, take the trail toward Little O'Malley Peak. This goes through some forest and drops into a creek valley with a bridged crossing. It then punches up a gully that can hold snow well into summer. Kick up the snow or zigzag the grassy slope alongside. The top of this gully is the saddle with Little O'Malley, and the ridge leading to O'Malley is opposite. The trail drops down, however, to a broad tundra valley called the Ballpark.

Enjoy a scenic romp gently uphill on a well-worn path, as the points on O'Malley's ridge tower overhead. The trail forks near the upper end of the Ballpark, and the way to go is to the right, toward a scree-filled gully leading up the mountain.

The trail more or less disappears into the rocks and possibly snow, but the only way to go is up. A few hundred feet of slogging and boulder hopping will get you to the notch in the ridge at the top. From there, a dirt trail reappears and leads along the south face of the mountain, bypassing rock bulges and one false summit on the way to the peak.

After one final scramble, you're there––overlooking all of the Anchorage bowl with mountains on every horizon, if the weather is clear. Nearer sights include lakes in the valleys on either side, and craggy ridgelines spanning in between.

Unless you want to explore a loop with another route, simply return the way you came. Glissading may aid your descent, depending on snow conditions in the gullies.

Sources: https://www.alaska.org/detail/omalley-peak-trail https://www.summitpost.org/o-malley-peak/536178