The dam is under construction and the road that used to run across the top of it is closed. That means that if you have a shuttle vehicle, it will have to go all the way around Boca to join you (or come in from town).
These fire roads are also used by motos, so avoid holidays and weekends if you want more quiet.
This is a great route to take if you are heading north of Truckee from the Tahoe-Pyramid Bikeway: Floriston to Hirschdale
and want to avoid pavement and that lengthy detour to town.
Starting at the Hirschdale exit on I-80, pedal the pavement upstream until you cross the river on the road bridge. An older bridge looks like great pedestrian/bike access instead, but there's no trail to it.
Reaching the railroad track on the other side of the river, pedal up a short hill toward the dam and immediately turn left into a large, ad-hoc parking area. On the other side of the clearing, take the small bridge across the dam outflow. The base of the bridge is open grating and the feeling is very airy!
On the other side, follow the user trail to a dirt road that switchbacks up and out of the outflow canyon, joining a short stretch of pavement before turning to gravel. Stay on the main gravel road past many spurs that often head to the reservoirs. There are road signs at the major intersections where you might get confused. You eventually cross the Commemorative Overland Emigrant Trail
and can join this singletrack to ride south toward Highway-89 or north to Stampede Reservoir if you like.
Near the end of the Old Reno Road, you'll start to hit patches of old asphalt before ending at the Russell Valley Road. Turn left to reach Hobart Mills, The Commemorative Overland Emigrant Trail
parking, or Old Highway 89 (East Pasture Loop #0886)