Great question! The McKenzie River Trail is one that is near and dear to my heart. I like to think of the trail as 3 different sections. The upper portion begins at Clear Lake. You can hike around the lake which is very beautiful (or rent row boats by the hour). The trail continues on from the southwest corner of the lake and before you know it you’re at Sahalie Falls and then Koosah Falls. These two waterfalls will impress you and the trail around here is very lush and picturesque. If you continue hiking down the trail you will notice that after a while the river disappears (it goes underground for a few miles). You can continue through this section, or after Koosah Falls loop back up the trail to your car at Clear Lake and shuttle to the next trailhead which would be at Trailbridge Reservoir. Take a right at the stop sign after you cross the river and head up the road to a parking area. Follow the trail on the right and in about 1.5 miles you’ll reach Tamolitch Falls aka Blue Pool. This is an out-and-back trail. If you still have time after these two hikes I would continue west on Highway 126 and stop at Belknap Hot Springs Resort. Here you can either give in to temptation and pay the $7 for an hour of relaxation in the swimming pool fed by natural hot springs, tour the beautiful property or hike a few miles down the trail (westward).
So the three sections in summary:
Upper McKenzie: Clear Lake to Koosah Falls (beautiful, scenic, waterfalls) Parking available at Clear Lake Resort, Sahalie Falls and Koosah Falls
Middle McKenzie: Trailbridge to Tamolitch (fire and ice, forest and lava, and beautiful Blue Pool)
Parking available at Trailbridge Reservoir
Lower McKenzie: Belknap Hot Springs to McKenzie Bridge (hot springs, and lush forest)
Parking available at Belknap Hot Springs Resort, Deer Creek Rd, or the McKenzie River Ranger Station