The soil surveys are pretty general. I would recommend auguring a hole to look at the soil first hand. If you moisten it and give it the ol' ribbon test, and get about a 2" ribbon or more, you might be in luck. The weathered bedrock reference is generally not good. If you hit bedrock, it will likely be very hard to seal. A very small crack can cause the pond to leak.

In looking at the aerial pic, it looks like the drain's side slopes are going to be pretty steep. That being the case, it would likely be hard to have an adequately sized emergency spillway without a bunch of dirtwork.

Looks to me like you could go down the drain into that open field and have a better pond site and an easier to build emergency spillway as well. With the steep channel slope up on that mountainside, the pond surface area doesn't look like it would be very big anyway.