The last two days I stayed at Lassen national park. You can find examples of different types of Vulcanos in the park. The highest peak is Lassen with ca. 3000m, the largest plug dome vulcano in the world,
there is Cinder Cone, obviousely a cinder cone vulcano and there is Brokeoff mountain, a remnant of a once gigantic stratovulcano that stood in the area and collapsed. There are active thermal regions as well.
The highway going through the park winds its way around Lassen peak climbing up to 2500m. The Northern side is not so special, mostly covered in pine trees hiding the views but the Southern side, essentially all the way from Summit lake campground to the Southern entrance station is very scenic.
And the downhill from the highest point to the Southern entrance is close to perfect: a winding road with very light traffic, not too steep to let you time to look around and admire the views,
but steep enough to let the average cyclist speed a bit (speed limits are sometimes as low as 15 to 20 mph, hence easy to over pass…) It has all it needs to leave a big smile in the cyclists face. At the campgrounds I saw a lot of cars with bikes loaded, but I saw non of them on the road. Why? Start at Manzanita lake climb up and let yourself roll down to the South entrance where you get picked up by your support car, seems to me a perfect half a day on bike.