Howell Mountain Road is short and sweet (steep), starting at Pope Valley and climbing to a few miles east of Angwin.
You really step deep into the past at the beginning of this climb.
This climb can be part of a 25 mile loop off of the extremely scenic (but busy) Silverado Trail, Napa County (map of loop). There is a bit of traffic along this road, but in our 4 times up the grade, we have always felt safe, with traffic passing slowly (and in low gear!). The tiny town of Pope Valley has a store with sufficient provisions to stock up for the next leg of any journey.