Well, you guys didn't totally poo poo the idea, so that's a bit encouraging.
I am examining two different ravines as possibilities. The first would be my ideal pond. Visible from a planned home site, about 2 acres in size, and a few branches to it. Below is the property.[Linked Image]

I guess it's more of a ravine system. I'm looking at the 810 contour. For a frame of reference, that picture is roughly
700 x 700 ft. or a bit over 11 acres.
There are several limitations I've learned. The first is this part of the ground is enrolled in a state forest and wild lands program, and I am limited to under 2 acres that can be modified into a water feature (pond). That's fine by me, as I stated 2 acres in my mind is ideal. The next limit is dam height. If my dam remains under 20ft in height, then no state gov. involvement is required. That sounds like a worthwhile goal too!
Then of course are the soil limitations. As both you guys noted, soil and bedrock need to be accounted for. Around the 780 contour, bed rock is exposed, as FishinRod guessed. Looks like a siltstone, and quite fractured. I'd probably try to stay above the 790 ft level because of that?
I am going to play around a bit with some software and info; it looks pretty powerful mapping this stuff out.