The Greenstone Ridge Trail is the backbone of Isle Royale, stretching approximately 40 miles across the full length of the island from Windigo on the west end to Lookout Louise near Rock Harbor on the east. Following the island's central ridgeline, it's the longest and most iconic trail in the park, typically completed as a point-to-point backpacking trip over 4–5 days.

The trail traverses the ancient basalt and copper-bearing greenstone that gives the ridge its name, winding through a mosaic of boreal forest, open ridgetop meadows, and rocky outcrops. Hikers gain sweeping views of Lake Superior's vast expanse, the island's inland lakes, and the rugged shoreline of both the Canadian and American sides on clear days. Highlights include the summit of Mount Desor (the island's highest point at 1,394 feet), the views from Sugar Mountain, and the quiet beauty of Lake Desor and Hatchet Lake visible below the ridge.

The trail is moderately strenuous, with rolling terrain and frequent elevation changes as it dips into forested valleys and climbs back to exposed ridgeline. While no single ascent is extreme, the cumulative elevation gain and rocky footing make it a legitimate challenge, especially under a full pack. Designated backcountry campsites and shelters are spaced along the route, and hikers must plan carefully around water sources, as the ridgetop can be dry between lake basins.

Isle Royale's remote wilderness setting — accessible only by ferry, floatplane, or private boat — makes the Greenstone Ridge Trail one of the most secluded long-distance hikes in the lower 48. Moose sightings are common, and the island's famous wolf population, though rarely seen, adds a wild edge to the experience. Blackflies and mosquitoes can be fierce from late June through July. The hiking season is short, generally running from mid-June through September, with the park closing entirely for winter.

The Greenstone Ridge Trail rewards those willing to make the journey to one of America's least-visited national parks with solitude, dramatic boreal landscapes, and a true wilderness experience surrounded by the cold, deep waters of Lake Superior.

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