This is kinda cool. Apparently, they had some sort of town spectacle in Tulsa, OK back in 1957. They buried a '57 Plymouth Belvedere under the lawn of the town courthouse. Inside is a steel container with a bunch of contestant's names and their guesses for the population of Tulsa in 2007, 50 years later. Winner gets the car and $100.
Yea, I agree with BP. Iron Oxide.
However, what if the water table in the area is really low, and moisture content of the surrounding earth is really dry. Hummmm.
If I remember correctly from the article, they will un-earth it in June. I put a note on my Outlook calendar for that day. I'll definately post a follow-up.