There is a dangerous log on the Dunsmier to Castle Crags run on the Sacramento. It spans most of the river a couple miles downstream of Dunsier where the river splits around an island. The log is in the right-hand channel.
It's dangerous because at some flows it is extremely difficult to see and looks more like a wave. At 5000 cfs on the delta gauge the log is a couple inches under water and you won't see it until you're right on top of it. At lower flows it should be more visible.