Sadly, the answer probably is - or at least was - Nevada. As the seventh largest state, it has a lot of real estate, most of which was utilized almost entirely by mining for precious metals. Gold and silver mining is usually intensive (as opposed to extensive coal mining, for example), pursuing a limited natural resource for a limited amount of time. This results in short-lived, explosive growth followed by a quick implosion of the community: because towns were typically built in places where there were next to no resources for survival, the lack of water and/or ground to farm caused most of these communities to be abandoned. The wealth that inspired the communities often inspired a few substantial buildings, which could survive the elements for a long time.

I write "sadly" because ghost town hunters from many places have used guidebooks as one might use a treasure map. They descended on the state and destroyed the historic resource so that many ghost towns, that were just as they were left even as late as the 1960s, were wiped off the face the earth and survive only as a spot on the map.

In almost all cases, these places are on federal land (which manages 87% of Nevada), so taking artifacts from a ghost town is usually a federal offense punishable under the 1906 Antiquities Act and/or the 1966 National Historic Preservation Act, as amended. When it is not on federal land, it is either public (state or local) land (so it is still illegal) or it is private land, in which case taking an artifact is theft.