Kinda funny this has come up. My father "winters" in Alamogordo every year. I told him the story of the buried cartridges a while ago. He has nearly hiked that entire region (literally). They had better have a pretty good idea where these are buried at or they "ain’t never gonna find 'em" quoted Pops.
I imagine tho, they could use some kind of ground penetrating sonar or such if they get an approximate geographical location. Even if they were capped by concrete. I highly doubt the local dump guys or contractors took any special care in completely eliminating all traces of the "Atari trash".
Which brings up another question. Did these have their own special "hole" that was dug and used (which would surprise me) or were they buried along with the local municipalities garbage and then capped? I've seen first hand what an 25+ year excavated dump site looks like. I don’t think people realize just how much crap goes into a local landfill or really how large they can get. Even for a smaller, less populated county (approx 45000 in 1980's) the amount of garbage in these is absolutely incredible. Now granted its a lot drier down there but you would be shocked at how much things can deteriorate underground. Especially if this stuff was buried with organic items.
Now if they did have there own site, then you would think that they would be fairly easy to find with all the zoning, parcels of land, tracts, permits and what not. All that info would be recorded in the local county court house...
I am betting there is nothing down there and it has all been a diversion. All that crap, if there really was any, and if it didn't get melted down in Cali. is in several cement filled shipping containers just outside the U.S. zone of territory off the California coast. Like someone said earlier, there is no way in hell Atari would ever have wanted this stuff found again.