From the Fourth of July trailhead on the north side of the parking lot, follow the signs for the Arapaho Pass trail Photo #1 to start. The trail starts out with a gentle climb Photo #2. There are plenty of social trails, side trails, and closed-for-rehabilitation previous trails, so stick with the clear and heavily trodden trail when in doubt. The trail climbs about 500 vertical feet in easy class 2 terrain Photo #3 in the first mile. Step carefully over various small streams.
Around 1.1 miles at 10,750 feet you reach the junction of the Diamond Lake trail. Stick with the Arapaho Pass trail Photo #4.
At 1.5 miles, around 11,100 feet, the trail goes almost level for half a mile of beautiful scenery Photo #5. At 2.0 miles and 11,200 feet, you’ll reach the ruins of the old Fourth of July pit mine and the juncture of the Arapaho Glacier trail Photo #6, a much smaller trail than the Arapaho Pass trail. Take care to make this right hand turn onto Arapaho Glacier trail.
Within a few feet cross a substantial stream or marshy area Photo #7, pass a large boulder Photo #8 and then continue your ascent Photo #9 Photo #10 gradually gaining altitude. You’ll pass through 12,000 feet about 3 miles from the trailhead Photo #11. South Arapaho Peak’s summit comes into view shortly thereafter Photo #12.
Continue on the Arapahoe Glacier trail (Photo #13, Photo #14) to the saddle at 12,700 feet Photo #15 between South Arapaho Peak to the west and Old Baldy to the east. Enjoy the view from the saddle looking down on the Arapaho Glacier itself. You are about 3.8 miles from the trailhead.
Leave the Arapaho Glacier trail (which heads east across Old Baldy) and head west toward South Arapaho Peak’s summit. From here, the dramatic point visible is a false summit. There is a visible trail if there is no snow. Pass the wind shelter on the west side of the saddle and ascend just to the left of the ridge line.
The terrain becomes more difficult here and to keep it as class 2, you’ll have to pick your route carefully and look for the cairns (Photo #16). Comfort with a few class 3 moves gives you some more flexibility in route over the rocky scramble (Photo #17). Generally, stay just inside the ridge line and keep ascending.
Reach a rocky knob at 13,000 feet (4 miles from trailhead) and get a great view of the false summit (Photo #18). Continue to push up difficult class 2 terrain (Photo #19, Photo #20). Reach the false summit and get a view of the true summit of South Arapaho Peak (Photo #21). Cross more Class 2 terrain (Photo #22). Photo #23 looks back on the route from the false summit to the true summit of South Arapaho.
Reach the summit of South Arapaho Peak at 13,397 feet and 4.3 miles from the trailhead. There is a small wind shelter, and just east of that, an engraved metal disc with names of nearby peaks and distances to them. North Arapaho Peak’s summit is beautifully visible from here (Photo #24) across the Class 4 traverse (Photo #25), and the Arapaho Glacier sprawls below, feeding Boulder’s water supply.