Last summer Ed and I took a side trip to Gato and among other things inspected the beautifully preserved stone pump house there. Inside was a small vertical boiler and reciprocating engine to run a water pump....all well preserved. At some point the plumbing had been rearranged to accomodate an electric pump. I would not be at all surprised the Bondad arrangement might have been similar....although Bondad was a newer installation and perhaps did start with some kind of distillate engine, as Earl suggests.
The stuff at Gato cries out to be protected or moved....although moving a stone pumphouse would be a chore.