Just returned from my best backpacking trip ever in the Goat Rocks Wilderness area in between Mt. Rainier and Mt. Adams in Washington. I was there July 27 – August 1 and the weather was as perfect. The mosquitoes were a bit aggressive but manageable. Overall the trip probably included about 33 miles and 5000 ft of vertical. I have returned to Goat Rocks with less favorable results as with my Smokey Trek in 2018. The loop option I chose was from the Berry Patch Trailhead heading up the Snowgrass Trail to the bypass over to the PCT. That section of the PCT gives you good campsite options with access to Cispus Pass and Old Snowy.
Typically there will be a good snow fields to keep you cool as you hike to Old Snowy.
When you have tired of the PCT portion of the loop take the short trail link over to Lilly Basin and continue on to Goat Lake.
This video of the falls below Goat Lake tries to convey the enormity of the area.
The campsite below Goat Lake is primo, however, there are many spots up and around Goat Lake.
The loop continues on the Lilly Basin Trail joining the Goat Ridge Trail but you may want to continue a bit further on the Lilly Basin Trail up to Hawkeye Point. The return is all down hill and you do tend to run into serious bug stretches as you reenter the trees.