A common type of North American Historic-Era archaeological site is the can scatter. These are exactly what they sound like, and most of the time are not anything to get all that excited about. However, every now and again, we find some that are associated with groups such as "Oakie" migrants from the Dust Bowl, or Filipino immigrant workers - in other words, people for whom we have very little first-hand information from the historic record. In these cases, a material record of where they were, what they did when they got there, and how the may have thought of themselves and dealt with their conditions is of great value.
A member of the crew on my current project told me of something that happened some time back involving a historic can scatter. They had been performing archaeological surveys along the major roads of southern California and came across one of these types of sites. They marked the point on their GPS units and kept moving, their plan being to return to the site after they had finished survey in order to record it.
As planned, they returned to the location a week later, ready to record. They followed their GPS units to the location, and found nothing. They thought at first that their GPS unit was malfunctioning. So, they tried a different unit, same problem. They then figured that they would simply pick a point where they knew they would be out of the site area and walk their survey line back towards the site, and they still couldn't find it. In the end, they had to admit that the site had simply vanished.
Doing research a few days later the crew found out that a local Boy Scout troop had, as a community service project, been picking up litter in the area and hauling it to the local dump. They had simply taken all of the material from the archaeological site and hauled it out of there.
Damn Boy Scouts, always up to no good...