Way out in the heart of the Boise National Forest is this gem of a trail. Once you begin from the very top of a narrow mountain pass and climb up the first steep (17% grade!) and rocky climb there's no turning back (use a shuttle).
After the first climb, the trail rips down the contours of Corbus Creek. It's a narrow, fast track and at points there is quite a bit of exposure off the right side down the steep meadowy creek bank. In the early summer the meadows are filled with yellow and purple flowers making it a hard choice between bombing the DH and stopping to smell the flowers and take in the views.
The trail descends down 4 miles or so before coming to a creek crossing and the 2nd of 4 distinct climbs. This one is the shortest of the 4, but it still features a 17.6% grade. It is followed by a quick descent with exposure nearly the whole way down to a tributary of the Yuba river.
Climbing back out of the creek valley is the 3rd climb, which is less steep than the others but is also twice as long. Following the pattern of cresting a ridgeline and descending into a creek bed, the trail zips down more smooth singletrack before the final climb.
The final climb is by far the most fun as it follows the contours at a much more gentle grade and is less of a grind fest than the previous three. Catch your breath at the top of this one because the final descent requires focus. Plus the views of the remote wilderness are rather humbling. The ride down to the Yuba River is loose in some spots, has some tight switchbacks, and has a lot of exposure to a steep rocky slope. Get your head straight, check your brakes and rip it!