The Summit Lake Trailhead is located at the Summit Lake Ranger Station, 17 miles north of the southwest entrance or 12 miles southeast of the northwest entrance. You may also pick up the Summit Lake trail from the South and North Summit Lake campgrounds.
Lassen Volcanic National Park: A Complete Hiker's Guide by Mike White
Lassen Volcanic National Park: A Complete Hiker's Guide
The trailhead is at Summit Lake along Highway 89. This trail offers a variety of hikes, out and back as far as you would like, or a loop past 10 lakes connecting with the Pacific Crest Trail. This is a very nice area to explore on foot.