A well placed rifle shot to the shaft - preferably near the gears - would cause it to "freeze up", kind of like what happens to the alternator in your car when metal bits come loose. In theory, doing so would make it come to a complete stop without sudden external trauma and subsequent flying debris. Can't know for 100% certainty until a marksman actually tries it though.

But it does bring up a larger issue regarding wind turbines - potential of exposure to sabotage. Unlike hydropower, nuclear, coal, and natural gas turbines (all of which are enclosed in solid structures), wind turbine mechanisms have no containment structure surrounding them. Anyone from a distance with a good aim could take them out of commission, not that any electricity customers would notice - all wind power has to be backed up by conventional power sources anyway due to wind's inherent intermittency/unpredictability. Taking out a wind turbine results in no net loss of generation capacity.

BTW - what does this have to do with railroads? Did the railroads through Tehachapi get shut down too?