sandy/gravely bottom land
thousands of little sand piles
holes nearly contiguous, maybe a foot apart or so.
holes adjacent (to the side I assume)
holes smaller than an inch
This
thread is rather old but I think I know exactly what you had found.
Probably not crawdad holes in sand and they would have a hole bigger than an inch. Crawdad holes are also usually pyramid shaped with the hole at the top and not adjacent or to the side of the mound.
What you ran across was likely a cicada killer colony. They are a large wasp about 2 inches long. They make these tunnels, catch a cicada wich they sting and paralyse to lay eggs in, put them in the tunnel and then they disappear until the next year. The tunnels are usually not around for more than 3 weeks maybe from what I have seen. They will be in a colony with holes everywhere. The wiki says their range does go all the way from the eastern US to Mexico. I've spent a lot of time in the woods and fields and I have only ever seen 1 colony so I think they are somewhat rare, though the colony is in the same place every year.
Here is a good wiki article on them. There is a picture to the right of the article half way down or so showing the mounds all over a
yard.
http://en.wikipedia.org/wiki/Sphecius_speciosus