Wednesday, September 7, 2011

Serendipitous geology

I can't believe it has been over a month since I last posted anything...well I can believe it I guess. It is a combination of it being summer and constantly on the move and being a bit lazy when it comes to posting.

Last week I was poking around an un-excavated Pueblo III site in the Montezuma Valley near Mesa Verde NP. I am quite used to looking at cliff dwellings all around the 4-corners area, this was the first Pueblo aged, non-cliff dwelling that I had spent any time in. What struck me first was that the Mancos shale does not have much of the favorite building materials- sand stone blocks. The Mancos shale is an incredibly deep layer of marine sediment left over from the Cretaceous Seaway. It is not known for it's sandstone building blocks. However, as the inland sea retreated somewhat, there were deposited three units that can be used for building blocks: the Point Lookout sandstone was deposited followed by the Menefee formation, a coastal plain region and a local source of coal and lastly the appropriately named Cliff house sandstone. The Cliff house is where most of the famous cliff dwellings are found.

However, the Montezuma Valley is dominated by the Mancos shale.

Lucky for the former inhabitants of this little pueblo the Menefee formation, is not only rich in sandstone but has a habit of slope failure creating sandstone deposits on the valley floor. The search for local building materials just got easier. A little bit of driving around the nearby county roads found a potential sand stone quarry.

To be a more complete geology day and completely overshadow the archeology was the discovery of fossil shells in the sandstone building blocks. My knowledge of paleontology is quite limited and I won't even hazard a guess at the names of the fossils we found.

A section of wall peeks out from beneath some vegetation with Mesa Verde in the background.

Some of the pottery shards found near the site.
A chunk of ancient building materials complete with even more ancient fossil evidence.
...and more
A close up of the surviving Pueblo wall.

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