This marking is incorrect  This is not the Boca Damn,  The Boca Damn is where the Little Truckee River and the Reservoir meet it is not up the river from it.  

This is the Historical site of the town of Boca

Boca:
Years: 1866 - 1939
population: 300
post office: 1872 - 1945
notes:
Boca Mill & Ice Company
Union Ice Company
Boca Brewery
Hotel, School, Stores, Saloon,
the damn was built in 1939 and the remaining buildings were demolished

for more information:
https://youtu.be/XDSansmhY0E