This backpacking trip to Garnet Lake is recommended over 3 days / 2 nights. Enjoy secluded camping and spectacular mountain views.
Although this trip specifically describes how to get to Garnet Lake, there are several other pristine alpine lakes (Shadow Lake and Thousand Islands Lake) along this looped trail, only a few short miles away from each other, that are just as worthy if you have the time. A minimum of 3 days/2 nights is reccommended, but you can tackle this trek in a day if you don't have the luxury of time.
To pitch a tent, sip some spirits, and sleep under the stars at Garnet Lake, you want to start by parking at the Mammoth Mountain Village, where you can take the service shuttle to the Agnew Meadows parking lot/trailhead. The Agnew Meadows Trailhead starts at an elevation of about 8,400 ft. and dips into a canyon along the John Muir Trail at about 8,100 ft. Following the river trail along the canyon floor, you will continue tramping northwest past Olaine Lake to a fork in the trail. This fork is the start of a big loop - to the left is Shadow Lake Trail which leads you to...you guessed it, Shadow Lake and onwards to Garnet Lake. It's a fairly steep incline, but provides you with a magnificent backside view of Mammoth Mountain and the river valley you were just hiking through. You can also go right and follow the trail north along the river to Thousand Islands Lake. You can reach Garnet Lake either way.
Once you've tramped up to Shadow Lake (8,770') from the fork, this marks your halfway point to Garnet Lake. 3.5 miles down, 3.5 miles to go. The trail winds around the shore of Shadow Lake and elevates through a series of switchbacks topping out at about 10,000+ ft. This section of the trail provides stunning views of the Minarets and the Ansel Adams Wilderness - there are several lookout points which are perfect spots to relax and have a picnic, or snap photos of the Minarets. The pinnacle of this trail will lead you up to the tree-line and provide you with a breathtaking view of Garnet Lake (9,710') with Mt. Ritter (13,143') and Banner Peak (12,936') standing tall in the background. From here, hike down to the lake and pitch a tent anywhere you'd like out of view from the trail. Happy tramping!