This is something a little different, leading to something cool: the NW Geology Blog has assembled quite a few self-guided geological fieldtrips, mostly in the Seattle to Vancouver corridor. There are two in the Fraser Valley: the Aldergrove glacial erratic, and the Shasta erratic in Coquitlam. The other BC field trip is to the recent, massive debris flow at Capricorn Creek.
But it was one of the Washington State trips which caught my eye though: a trip to a formation of Stilpnomelane at Blanchard Mountain, Skagit County, near Bellingham Washington. The reason this caught my eye: the formation is intersected by massive, green chert beds.
Chert is a silica rich, micro-crystalline rock which can be extremely well-suited for making stone tools. Not all chert is created equal – it can often be brecciated or have internal, blocky fractures. But the chert illustrated in the NW Geology blog seems to occur in quite large beds and nodules, and I would be surprised if there wasn’t useful material in there. As you can see from the view below, it is very close to the ocean, and the mountain must have been well-known and used for a suite of different resources. As it happens, we worked at some sites this summer in the Salish sea where green chert artifacts were not uncommon. As the crow flies, Bellingham is quite close to Portland and Sidney Islands. Green chert is also widely known from elsewhere on the south coast. I have no idea whether or not the Blanchard Mountain source was used, or even usable – it is exposed in a recent road cut – but it might well be worth following up, assuming the Washington State arkies aren’t all over this already. Chert is not that common, especially in larger nodules and beds – which, on Blanchard Mountain, could also be a source for chert found in glacial deposits elsewhere. There is a short technical report on this formation here, also. There has been some recent research demonstrating the ability to chemically fingerprint cherts, which raises the possibility of nailing down a connection between the archaeological record and certain cherts (ref 1, 2-pdf) as is widely down for obsidian.
It is also intriguing that Blanchard Mountain is home to greenstone and greywacke and semi-schist, the latter two which may be what is commonly called “slate” in the archaeological record. There is also a major cave system – “almost infinite twisted passageways”. Caves can be attractive to animals and thus to humans, and can also be very stable repositories which preserve archaeological material indefinitely. They are therefore one of the highest-potential geological formations in which to find archaeology from the very early period on the coast, where other landforms see much destructive erosion. This blog post tells you a little about some other rocks and how to get to the caves.
Anyway, it is a nice blog and the author, Dave Tucker, is also writing a book which, if his well-written posts are anything to go by, should be well worth having.