Thompson Peak is the highest Peak in the Trinity Alps Wilderness, a vast assemblage of craggy granite mountains in northwestern California (Trinity Alps Wilderness is the second largest designated wilderness area in California). Thompson Peak is the second highest mountain in Northern California west of the Cascades, after 9027 feet Mount Eddy. Per SP member Ed Cooper "It is incorrect to say that there is no longer glacial activity in the area. The Thompson Glacier lies below the North Face of Thompson Peak. Late in the season, when most of the winter snow has melted, the crevasses and ice of this glacier are exposed. There is another smaller body of snow/ice to the right of the Thompson Glacier, below the north face that might also be considered a small glacier. Further, there is definitely one small glacier on a nearby peak that has crevasses and clearly displays glacier ice. The Trinity Alps have the distinction of being the only mountain range in the United States that lies entirely below timberline (small trees grow just below the final summit block of Thompson Peak) that contains active glaciers."