The Amgen detailed Stage 2 map, now online, shows a route through the outskirts of both Nevada City and Grass Valley.
More details may prove parts of the following guess wrong, but — judging only by the online map, which is still somewhat crude — the route approaches (but misses) downtown Nevada City on Highway 20, then onto Nevada Street, to Sacramento Street, to Zion Street and onto to Ridge Road all the way to Grass Valley.
The race continues on Ridge Road, missing downtown Grass Valley proper, and on to Rough and Ready Highway, rejoining Highway 20 at Penn Valley, then continues on Highway 20 all the way to Beale AFB and beyond.
Here’s the relevant portion of the map (see the whole dynamic map here):
Here’s the Stage 2 video, just released: