Another in my Trimountain mining system caches. This is at the bottom of an earthen dam. At the bottom of the dam you will find a series of concrete bases. I think there was a pumping system to pump water back to the #1 boiler house (track the foundations to the SW to find it). Also it probably supplied water to the #2.
Come to this as you will, but the trailhead will make it Much easier. My standard container