Many North Cascade hikes require some tradeoffs for views of the so-called “American Alps," whether in the form of long, bumpy forest roads or long, knee-busting trails that are only accessible a few months out of the year. Not so with Thunder Knob. This ominously named trail is much shorter and easier than it sounds, at only 3.5 miles round trip. Best of all, there are no forest roads to worry about because the trailhead is right off Highway 20, and the hike is accessible year round.
Thunder Knob trail begins at the north loop in Colonial Creek Campground. This location makes it a great option for campers, who can walk from their site to the trailhead in minutes. From the parking area, head north past a few campsites to cross a bridge over Colonial Creek. Fed by Colonial Peak's glaciers, the creek flooded in 2003 and 2006, causing irreparable damage to several campsites. Walk through the rocky, dry creek bed before entering a forest of western hemlock.
At 1 mile, views open up to Colonial Peak in the south. The landscape begins to change here: hemlock gives way to lodgepole pine, and the soil becomes noticeably drier, both effects from the rain shadow. At a junction, head left for the first of two Diablo Lake viewpoints. Davis Peak and McMillan Spires are visible to the west, while Sourdough Mountain rises from Diablo Lake directly north. Back at the junction, continue to the second viewpoint for a glimpse of Jack Mountain through the trees. You can even peer down on Diablo Lake Overlook from here.