Clear Creek Route to Mount Shasta is a 16.8 mile lightly trafficked out and back trail located near Mccloud, CA that features a river and is only recommended for very experienced adventurers. The trail is primarily used for hiking, camping, and backpacking and is accessible from June until October.
Can be done as a day hike, would be difficult. There's a perfect little meadow for a base camp about 5 miles in with a spring fed creek. This only leaves about 3 miles, 6000 feet of vertical still, to the summit. There is a trail most of the way up until about 1500 feet below the summit. From there it's a scree scramble. When you get to the headwall, about 200 feet below the summit, we went up a fan to the right of the wall. Some class 2/3 bouldering could probably get you up easier but we were too tired and hit dead ends/too technical of a climb the first two routes we tried.
Loved this climb. Shasta is thousands of feet taller than anything in the vicinity so it's almost as if you're looking out of an airplane window, down at the rest of the world. Very peaceful, stark and beautiful. Be prepared to work for it, it was a 15 hour day for our group to summit, break down camp and get to the car before we were chased out by a thunderstorm.