Between Sierra City and Downieville. I nearly crashed there yesterday. There are a couple of marked one-lane zones where they're doing construction improvements, but you won't know about the third at Ladie's Canyon Creek bridge (https://www.google.com/maps/@39.5687258,-120.721828,3a,75y,347.36h,72.89t/data=!3m6!1e1!3m4!1skcSmQV1pp5HHBy14UxgM_A!2e0!7i13312!8i6656?hl=en) <== Google Maps image.
They've added a fresh layer of concrete, so you'll bump over it coming and going from the blacktop surfaces, plus they've put some sort of releasing agent or sand on it. Two of us had a little or a lotta wobble going over it.
Take your enthusiasm level down a notch or two there. Treat it like a sand zone and you should be fine.
kinda sounds like the same thing from Portola to Quincy to Bucks Lake. Was there on Wednesday and Caltrans was nice enough to be doing tar snakes that day. Up to Bucks Lake was sandy and dirty. On the way back, NDOT was nice enough to be doing painting...made for an interesting day of riding. And holy cow...the burnt areas from the recent fires. Good Gawd!
Nothing like trying out the steering dampeners!
Heading there this weekend.