| Hi Steve- I'm not sure how far into zone 7 they're hardy, but I've had good luck with Habranthus tubispathus in conditions such as the ones you describe. They're also called Texas Copper Lilies, and they do most of their growing in the winter when water is available, then put out blooms as the rains come during the summer. They also reseed like crazy here in coastal VA. Another possibility is Zephyranthes drummondii (sometimes listed as Cooperia); it's a pure white flower with glaucous foliage that seems to take very hot, dry conditions. A good source for these bulbs and info is Yucca Do nurseries (I think it's just yuccado.com). I would think that any of the crocus, fall and spring bloomers, would also do very well in a scree bed, as would Cyclamen hederifolium and Sternbergia lutea. I'm also finding Cyclamen purpurea to be very well adapted to growing in zone 7b, with the added benefit of being essentially evergreen. Species tulips might also be a good bet; drainage here is such that they don't prosper for me except under scree conditions. A great book for this sort of info is "Garden Bulbs for the South" by Scott Ogden - the second edition was released last spring, and I recommend it highly. | 
