I discovered this plaque and the remains of the line while prowling around the El Tovar hotel at the south rim of the Grand Canyon.
It looks like this was built with water pipe! Note the pipe "pole" and "crossarm", and lack of insulators. (If you follow the link that Bart provided, below, you can see insulators in the construction photos.)
Try "view original" for more details.
Later in the evening Bart Magoffin sent me the following: Think I posted something about this on ICON last year. We visited the GC then, even walked the trail there and did Not see the marker. Darn. Good thing maybe, I may have fallen in trying to see an insulator.
Here is a link, nice old pictures: http://www.geocities.com/shioshya/ccc/index.htm
I followed the link and the pictures are terrific! I snagged copies of them, in case GeoCities goes away and they become unavailable. I posted them starting here: [id=261098183]