Mystery circle at Wisp

A friend was recently visiting Wisp and noticed a large concrete circle painted black on the top of the mountain. Does anyone know what this is? A link to Google Maps showing this is at:

http://tinyurl.com/32872nd

Hmmm...does not look like concrete to me. It looks like it has ribs...

Perhaps a water tank. Sort of reminds me of the one at Timberline.
The Colonel

500,000 gallon water tank. The more interesting question is how this relates to the snowmaking system and the ASCI whitewater course, if at all, or whether it is just for residential use. This is the highest point on Marsh Mountain.
Water article

My GUESS would be that it relates to the white water course than can be filled and turned into a rushing river!
The Colonel

It is a water tank that is for residential use. It is not used for snow making or the whitewater course. I own a home on Highline Drive, on the Main Street ski slope, and that tank serves my neighborhood as well as the others on top of the mountain.

DJ beat me to it. That water tank services my neighborhood at Villages of Wisp also.