Diamond Lake is a pristine natural reservoir carved out by millennia of slow glacial movement and filled by meltwater. It is one of many similar lakes in this region of the Rocky Mountains west of Boulder, Colorado, but this one makes for a particularly scenic hike of moderate length and difficulty. Highlights of the trail include wildflowers, waterfalls, wildlife, and, of course, the lake itself.
The trail is accessed from Fourth of July Road, which is named for an on old mine in the area. The road is long and bumpy, but is passable for two-wheel-drive passenger cars. Camping is here is free, but limited, at Buckingham Campground.
Begin the hike at Fourth of July Trailhead on the Arapahoe Pass Trail heading up the valley to the northwest. At 1.2 miles the Diamond Lake Trail turns off to the left and drops down through the valley to cross Middle Boulder Creek near a very pretty waterfall. From here, it is approximately one mile to the lake along a northeast-facing slope that can hold snow throughout the spring and well into the summer. Be prepared for some route finding if the trail is still covered. There is a signed turnoff for Diamond Lake.
Most parties end their hike here, and it is indeed a worthy destination. However, by returning to the main trail and continuing uphill you can forge on past tree line to a high point of 11,400 feet. This section of trail beyond Diamond Lake is 2.4 miles to the intersection with Devil's Thumb Trail, where a longer linkup will get you to Jasper Lake and Devil's Thumb Lake
Note: For overnight camping at Diamond Lake or anywhere within Indian Peaks Wilderness, a wilderness overnight permit for the Diamond Lake Backcountry Zone is required between June 1 and September 15. Contact Boulder Ranger District at 303.541.2500 for details.