If you look at a California Department of Parks and Recreation Form 523 Primary (see it here), the one required for recording archaeological sites in California, you are giving three options for the site's age: Prehistoric, Historic, and Both. This seems straightforward - if the site pre-dates the introduction of written records (literally predates recorded history) then it is prehistoric, so everything prior to Europeans showing up; if the site post-dates the introduction of written records, then it is historic; if the site has elements from both before and after the introduction of written records, it is both.
Of course not.
I'm not going to wade into the debate about whether or not oral traditions should be considered history. It's a valid line of debate to a point, but not what I'm interested in here. What I am interested in is what we use to make the distinction between prehistoric and historic sites, why the three check boxes aren't maybe the best way to reflect the archaeological record, and what's they ultimately mean.
For starters, when we record a site, the way that we identify which of the three boxes to check is be evaluating what materials are present within the site. If it is filled with flaked stone tools, ground stone tools, and no evidence of metal, glass, or European-style tools or structures, it gets labelled "prehistoric"; if it contains things such as milled wood, metal, glass, paper, etc, then we label it "historic" (and, obviously, if it contains elements from both categories, then we label it "both").
Here's the problem: The prehistoric/historic dividing line in California (and much of the world, in fact) is murky at best, and nonexistent at worse. The introduction of written records to California came with the Europeans. The problem, of course, is determining when you should place this. Should it be with the early voyages in the 1540s? Should it be with the founding of the missions in the 1760s through the 1820s? Should it be with the establishment of Euro-American settlements in even the more remote parts of the state in the 1890s and 1910s?
The practice that we have been in is to ignore all of these potential dates and look insteadm as described above, just at what's present in the site. The problem here is that this results in sites that were occupied by people well-documented in the historical record being labelled "prehistoric", which is just plain factually incorrect. There are other, more correct, labels available: ethnohistoric, protohistoric, etc. All of which are in active use in research archaeology, but not available as a check box on the documents that we are required to use.
What's more, there's a tendency to associate "prehistoric" sites with Native Americans, and "historic" sites with everyone else (Euro-Americans, African-Americans, Asian-Americans, etc.). But this really isn't correct, either, as Native Americans did adopt many of the materials from the newly-arrived groups, and so it is not uncommon to find a Native American site from the late 19th or early 20th century that is comprised of a wood-frame house and glass and metal detritus, similar to the non-Native homes of the day. There would be differences in the material patterning of the site, just as there are differences between the sites of Italian immigrants vs. German immigrants, but it would still end up being given the "Historic" label (maybe a "both" label if things such as ground stone were found on-site, but the ground stone would often be assumed to have pre-dated the rest of the material, even thought it didn't necessarily), and unless there was a clear record that the home belonged to a Native American, there would typically be little effort made to determine to whom it belonged.
Up to this point, this has probably all seemed like pointless ranting about something that is unimportant. So, I'll try to explain why this actually does matter.
Under current practice and regulations, Native Americans have a more significant role when a "prehistoric" site is found than when a "historic" site is found. The reasoning seems pretty clear - the prehistoric site belongs to their cultural lineage, whereas the historic site is seen as belonging to the post-European cultural lineage. But the problem is that, as describe dabove, many historic sites are Native American sites, and so it seems rather bizarrely inconsistent to only consult with them on prehistoric sites when they may have relevant information on historic sites as well.
Now, many of my colleagues will point out that sufficient background research will identify historic-era sites that are the homes of Native American individuals and families. This is generally true, but because of the nature of late 19th/early 20th century racial politics, it's not uncommon for ownership information or ethnicity identification to not be readily apparent in this historic record.
The reality is that the division of prehistoric and historic, while it annoys my inner fact-checker, does work the majority of the time. But that doesn't stop me from wondering how often we get it wrong, or when it is going to bite some (or maybe all) of us in the ass.