Ranch Girl, you may not have a hopeless situation with the clay down at 15 feet. here's what came to my mind... how big of a place do you have to build a pond? here's why. if you plan to build a biiiiigggg dam, then you will need a lot of back fill on the back slope of the dam. now, if you are building a biiiigggg dam, i.e. in a ravine or whatever, you may require a lot of back fill. so your dozers would scrape the top 15 feet or so off (which i admit, is a lot, probably too much), and place that top dirt layer where the back slope area of the dam is to be. then, the clay would be exposed and the experience dozer guy (or girl) would then use that for the trench and front slope, bottoms and sides of the pond/lake. if you plan to build a small pond, your best bet may be a liner, or hauling in clay/bentonite. hope this helps.
one more thing...you may want to build your pond first, get an engineer or surveyor to come out and "shoot your lines/slopes/water levels" so you know where the water levels will be etc. now, before i invest much time/effort/money into those big trees/moving them...i personally would make sure your pond holds water and fills. then do the add-ons/ touch ups later. mark
