My experience at the Trona,Ca dumpsites..
The dumps were shut down in 1954. Locals have been collecting artifacts from the site since then. The easily accessible sites have long been emptied. But there remain areas where people during the late 1940s/early 50s dumped bricks,cement blocks,etc that covered up the oldest dumpings. No-one but me has been balsy enough to dig down thru tons of brick and cement to reach the bottom-most layer. This means braving poisonous scorpions and the ocaissional rattlesnake. But down there 'neath it all are artifacts,marbles,tokens and such that were never subjected to fire. As pristine as the day they were made some dating back to 1875. I have braved 130F heat,hurricane force sandstorms and flash floods.