Elevation : 1,240 ft
The Thunder Creek Trail begins in ancient forests and takes the hiker on a sojourn into the heart of the park, following the cloudy-Blue, Glacier-fed creek from its lower forested reaches to its origins high on the heathered slopes of Park Creek Pass. Day hikers can take an easy stroll two miles (3.2 km) to the first bridge, or do a longer, more strenuous hike up to Fourth of July Pass or farther along the main trail. Backpackers enjoy the lower reaches of the Thunder Creek Trail as a shoulder-season getaway, or mid-season as a multi-day trip up and over the spectacular Park Creek Pass into the Stehekin Valley.
The first half mile (.8 km) follows Thunder Arm of Diablo Lake. Note the turquoise color of the lake and stream. This is because Thunder Creek carries a heavy load of “rock flour,” ground by the Many glaciers of its headwaters. This trail was opened by prospectors and trappers. Mining developers and the US Forest Service made major improvements in the Early 1900’s. Look for old blazes, and a few cut stumps along the way. At 300 yards (90 m) from the trailhead, a sign marks the Thunder Woods Nature Trail leading off to the right. This is a self-guided interpretive walk along a 0.9 mile (1.4 km) loop.
Follow State Route 20 to mile 130, Diablo Lake. Enter the south side of Colonial Creek Campground and park in the large lot above the boat ramp. Stock parties should access this trail via the trailhead that lies uphill from the parking lot behind the trailer dump station. This is the preferred trailhead for horses. Hikers and backpackers should walk the length of the campground, following the signs to the amphitheater, where the main trail begins.