Earlier today, I was reading a report on excavations performed in the San Gabriel Valley, which is one of the many valleys in the hills of Los Angeles County. It was noted in the report that there is not much information available in the archaeological literature regarding these inland valleys, and that most of the research done in Los Angeles County is focused on the coast and the Mojave Desert. In fact, if you were to look only at the published work, you'd get the impression that people lived in the desert and on the coast, and nowhere else in southern California, which is not actually true.
When I was working on my Master's Thesis, I encountered a similar issue in the Santa Barbara Channel area. Almost all of the archaeological research on the area was performed on the coast or, more often, on the Channel Islands. There was one excavation report that was only a few years old, one MA thesis that was ten years old, and a smattering of MA theses, doctoral dissertations, and articles that ranged in age from 25 to 40 years old, almost all of which contained woefully out-of-date information. In the Santa Barbara area, the focus on the Channel Islands is so pronounced that a recent book that is allegedly about the socio-political complexity of the Chumash (the native peoples of the area) has only one chapter on the mainland (focused exclusively on the coast, naturally) and otherwise focuses entirely on the islands, despite the fact that the majority of the people lived on the mainland and that the interior is a pretty big chunk of real-estate that is often vaguely invoked in discussions of the complexity of the area.
Talking with colleagues in other parts of the U.S., and even in other countries, it becomes apparent that this is a common problem: certain areas get the bulk of the attention, while other areas which are arguably equally important are simply ignored or glossed over. The end result is that our view of the history and prehistory of certain parts of the world is rather skewed.
Sometimes the skewing is due to simple site availability: if sites are located on private land, they are harder or even impossible to access legally; if an area is heavily urbanized, there may be very few sites left, and so only those still in fair condition can be examined; and in some places, the geology itself may be against you and the deposition of sediments during floods may cover sites and make them either highly difficult to find or else prohibitively difficult to access and study.
Other times, the skewing is due to site condition: We all like pristine sites, but in many places these are hard to come by. The California Channel Islands lack the burrowing rodents that are the bane of the mainland archaeologist's existence, and have also not been subjected to the urban development that mainland sites often have. As a result, they are very appealing...I would say too appealing, as this is one of the factors that has resulted in archaeologists extrapolating conclusions drawn about the very specialized island environment onto the mainland of North America. Likewise, archaeologists may be dissuaded from studying a site if it has been subject to ground disturbance due to construction, but that site, even with the disturbances, may still hold important information.
Another factor that shouldn't be overlooked is the location. Sites on the coast or in the mountains offer beautiful scenery. Sites in an inland valley may be hot and unpleasant. While most archaeologists won't admit that this influences their decisions in public, it tends to come out when we are talking to each other.
It should also be considered that people's research questions are influenced by what has come before. If your goal is to study the socio-political complexity of the Chumash, then the fact that nearly every article and book on the subject mentions the importance of the inland and interior as trade partners within the complex system doesn't change the fact that almost all of the research has been done on the Channel Islands on on large coastal villages, and as a result that is where you go to do such work. For example, another recent book on the subject of Chumash complexity did a decent job of placing more attention on the mainland - where most of the people actually lived - but still largely glossed over everything that wasn't on the coast.
And, of course, we shouldn't forget that most archaeologists want to find spectacular sites. Most, if not all, of us want to see cool stuff and work in neat places. And some (though thankfully not all) funding sources are more likely to fund research at known spectacular sites, even if the research might be better directed elsewhere. As a result, the inclinations of the researcher and occasionally the money may sway research towards places known to have cool sites even when the active research questions would be better served by looking into new or less-explored areas.
One added issue is that many of these less-spectacular locations have been subject to archaeological work via CRM archaeology - the sort of consulting work that I do - but this data frequently doesn't make it into the published research work. Part of the reason for this is likely that, in my experience, many academic archaeologists remain suspicious of CRM as a line of employment for those with "weak minds and strong backs" - an assessment that is inaccurate. However, many academic archaeologists are free of such prejudices, and yet find themselves confronted by the problem of the "grey literature" - the volumes of data and observations generated by CRM archaeologists which are deposited in information centers and archives, and which is difficult to navigate even for those of us who know how it's organized. As a result, there has been work done in areas that are under-represented in the published record, but which is never brought in to alleviate the problem because it remains unknown or hard to find.
I have focused on southern California because that is the area that I know the most about, but this problem is not unique to the region. I have spoken at conferences with archaeologists from across North America and even other parts of the world, and this issue has come up on nearly every continent. I don't know how to solve the problem, but simply being aware of it is often the first step.