The Arapaho Peaks are a very prominent set of peaks that stand as the tallest two mountains in the Indian Peaks Range. South Arapaho peak (13,400 feet) is the shorter of the two, but only by 100 feet, and they both are home to the largest glacier in the Front Range. North Arapaho Peak (13,500 feet) also holds claim to being the highest summit on the Continental Divide north of Denver. The easier of the two climbs is certainly South Arapaho Peak, which has the added bonus of getting better views of the glacier and North Arapaho Peak.
There are several ways to summit South Arapaho Peak, but the longest route and arguably the most scenic is the Arapaho Glacier Trail from the Rainbow Lakes Trailhead. This trail takes the ridge leading off the eastern slopes of the Arapaho Peaks and just to the south of the Boulder Watershed. Many signs along the path will warn you that the lakes and the Arapaho Glacier that feeds them are owned by the city of Boulder and is the main water source for the city. Anyone trespassing in the private area will be given a hefty fine.
Starting bright and early to avoid the limited parking and afternoon storms at the Rainbow Lakes Trailhead, follow the only trail up into the trees. You will soon see a signed fork in the trail. Take a right to stay on the Arapaho Glacier Trail, and that will be the last turn you have to make until you’re on your way back. The trail from here climbs steadily with some gentle ups and downs until reaching the treeline, which immediately opens up incredible views to the south, north and east. As you continue climbing the ridge, the views keep getting better. Continue on this trail as it undulates along the ridge until reaching the unsigned saddle between South Arapaho Peak and Old Baldy. It will be unmistakable, as Old Baldy is a big, flat open summit whereas South Arapaho Peak is a sharp mountain requiring a Class II scramble to get to the top.
From the saddle, make sure to evaluate the weather and take pictures of the glacier. The hikes becomes more difficult while scrambling the final 700 feet to the summit. Be forewarned of the false summit, which is a few hundred feet prior to the real summit. Continuing along the ridge to North Arapaho Peak is a 3-hour extra commitment with Class III+ scrambling, so take it on if you have the time, conditions and experience to do it safely. After enjoying the views at the top, make your way back down the way you came and take notice of the changing light as the day progresses.