The area in question is several 4-6 foot high X 20-30 foot long mounds of very sandy well-drained soil, lacking in nutrients. This soil was dug out to make an 8 foot deep pit (with 2 feet of water in it), and placed about 6 feet away from said pit. Unfortunately much of the sub soil (a grey, light gritty clay) ended up on the top of some of the mounds.
I'm in zone 5b but with the micro climate created I'd say this area is probably zone 6 or greater.
I haven't been able to find much useful information in my search. So far I've only found that I might be able to get away with Mulberry, Goji, and Persimmons (though I'm worried that the drainage will cause the fruit to drop prematurely). I read that " Extreme drought will cause the leaves and fruit to drop prematurely". If a really hot summer arrives, I'd be worried that this would result.
I have found both mulberry and persimon to be more demanding of high fertility(here in the pacificNW).I have had success with autumn olive and other plants in that family.Heartnut is adaptable to droughty conditions.Rubus sp. like raspberries can handle well drained.Bulbs that die back in the summer like camas work.
There is nothing permanent in a culture dependent on such temporaries as civilization.
I did some checking up on Autumn Olive and found some sources which say it is invasive. I wouldn't want to create another European Buckthorn phenomenon. Those things have spread all over the place in central ontario, all because someone wanted to grow them as an ornamental.
Go the library and request the Denver Water Boards' books on Xeriscaping. (They wrote three books, and made the word come into common usage, I think it is Greek for "without water".) READ!!! Denver is generally a zone 4 (and maybe gets warm enough to be a 5 or 6 with protection from wind and sun). These books will give you more choices than you have money or time for. I live in Northern Colorado, in the sagebrush, Zone 3, and I use them almost exclusively.
Oh and Brenda; I may resort to amending the planting area but thought that I could save myself the time and effort by finding a desirable bunch of plants that would do well in the existing mound, poor soil and all.
The list says pears, apples, and plums, which sounds good to me. If I plant them near the bottom of hte hill, they'd theoretically have greater access to water, still benefit from the heat of hte bank, and I could maybe harvest them from the top of the mound
Hmmm, sweet potato as a ground cover comes to mind actually. We're growing some in that same field in a 2 ft high beds, and they're doing really well, so I could see it working out with these giant mounds.