Use sunset as your turnaround alarm.
Amethyst is a proper cirque lake, 43.7 acres and 59 feet deep at 10,750 feet, which puts it in a different class from the roadside lakes off the highway. Getting there means turning east on Christmas Meadows Road, 0.6 miles south of the Bear River Ranger Station, then four miles in to a trailhead with vault toilets and horse parking. You follow the Stillwater Trail up the valley before the Amethyst Lake Trail branches off. The lake holds brook trout.
Gem of a cirque lake below Ostler Peak.
3 liters water or hydration pack, hiking boots, layers, headlamp, trail mix and jerky, trekking poles, first-aid kit.
Make it a weekend: Uinta Backcountry Lakes (Fishing, 5 mi) · Mirror Lake (Uintas) (Fishing, 8 mi) · Mirror Lake Campground (Camping, 8 mi) · Moosehorn Campground (Camping, 9 mi)
More hikes nearby: Ruth Lake (Hike, 7 mi) · Lofty Lake Loop (Hike, 7 mi) · Fehr Lake Trail (Hike, 8 mi) · Bald Mountain (Hike, 9 mi)