Broken Thumb is a nice diversion from the descent down Rollins Pass (aka Corona Pass). Broken Thumb could be ridden both ways but isn't that great of a climb and would likely require some walking. The upper portion of the trail is wide, fast, and flowy with water bar whoops and some steeper sections.
The bottom half is generally flatter and was reclaimed to singletrack in 2012 or 2013. From the trailhead on Water Board Road/ FS 128 head west (left if descending Broken Thumb) to get back to Rollins Pass (aka Corona Pass).