From Icehouse Saddle this trail begins from your hard right. The sign is sometimes hard to see due to trees. This trail is also one of the least maintained summit paths from the saddle. This can be good if you're looking for some solitude but thusly more dangerous if you're less experienced with hiking or even with this area in general. There are a few trail markers along the way, but if you're hiking in the off-season these can be hidden by snow and neglect. Follow the trail on up and you'll be granted a view of all the other summits in the area as well as a shot of the valley, smog allowing.
Henninger Flats is a small hanging basin 2600 ft above sea level in the San Gabriel Mountains in the Angeles National Forest. It was part of the Mount Wilson Toll Road. The trailhead to reach the flats is at the top end of Eaton Canyon in Altadena.