From the marked trailhead at 4,700', start climbing up the trail as it begins its journey towards Atascosa Lookout. The trail is relatively uneventful. You will pass through a gate, crest two small passes, and get a glimpse of a natural water tank along the way. The trail works its way along to the east side of Atascosa Lookout below the cliffs, then switchbacks up to the summit. After 2.5 miles, you will reach the top, which has a small building on it. This is a good place to take shelter during a rainstorm. You will also get your first glimpse of Atascosa Peak from here, located about one mile to the north. You must traverse north across the ridge to reach the peak. The elevation here is 6,249'.
From the top of Atascosa Lookout, go around to the east side of the building on the elevated walkway, and drop down to the ground. Then, start descending north down the ridge. This is the most difficult part of the climb. The terrain is steep, brushy, and rocky here, and there is no trail. You'll just have to drop down following the path of least resistance. After descending about 100' or so down the ridge, you will pick up a trail leading all the way to Atascosa Peak. This is not a maintained, but it is cairned. You'll have to drop down to the 5,920' saddle between the two mountains before starting up towards Atascosa Peak. Make the final push to the summit, where you can enjoy the desert views.
Hiking Distance: About 8 miles round trip.
Elevation Gain: About 2,500'.
Thanks for the great page on Atascosa Peak. I wanted to stop at the lookout cabin, so I followed the route you describe. But I also learned that the cairned route intersects FT 100 below the cabin, eliminating the nasty 1st hundred feet. The intersection is as described on the Geocache page (link in my summit log) for Atascosa Peak:
"Just after mile marker 2 ½ (broken sign) (at N31 25.283 W111 08.827), go left off the Atascosa Lookout trail onto a lighter trail. Follow this light trail for 1 ¼ miles with cairns to Atascosa Peak (N31 25.972 W111 08.815)."