The trailhead for Fish Creek Mountain can be found between the road and parking area, which is just a portion of a washed out road that is now blocked by dirt mounds. The steep, narrow trail climbs through an old-growth forest full of Douglas fir, red cedar, and western hemlock. At about 0.65 miles, the trail levels out. Turn right at a cairn to follow along another old road for about half a mile. Head straight up a dirt ridge, leaving the road that continues to the left, to find trail #541.
Find a volcanic dike after about 1.3 miles; here you'll get an incredible view of Mount Jefferson and the surrounding area. It's a steep climb for about a half mile after the dike, and in the summer you'll pass innumerable ant hills swarming with black ants along the trail. You'll find a fork in the trail about 0.7 miles from the dike, and you can split off to the right to descend to High Lake or continue straight for a half mile to the summit of Fish Creek Mountain.
Along with the sweeping views from the summit, you'll find the remains of an old fire lookout built in 1933. On the way back to the fork to High Lake, keep an eye out for views of Mount Hood peeking through the trees. The descent to High Lake is about 0.7 miles, and there are a couple of nice campsites that can be found around the lake. The lake is good for fishing and a swim on hot day.