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Mortar Rock Park, Berkeley

February 12, 2011
Mortar Rock

Mortar Rock


I spent much of the holiday period visiting family in California, staying in Berkeley, which is a city I like a lot. To the north east of the downtown area and UC campus, the orthogonal grid of city streets gives way to curvy residential roads which wind their way around outcrops of volcanic rhyolite and give stunning views over San Francisco Bay. Some of the larger outcrops have been set aside as parks, and bear names which are particularly inviting to the archaeologist/tourist – names like Indian Rock Park and Mortar Rock Park.

At Mortar Rock Park, mortars which were worn into the rock by people grinding acorns and other seeds can be seen. There’s an information sign that explains the site, but it is left to the visitor to find the individual holes, which I quite liked as it made me feel like I was being an archaeologist on my vacation. The signboard itself is interesting – it’s quite rich in ethnobotanical detail, but it doesn’t really tell you anything about the “Native Americans” (presumably the Ohlone people) who used the site, or when it was in use.

Information Sign at Mortar Rock

Information Sign at Mortar Rock

Mortars at Mortar Rock

Mortars at Mortar Rock

More mortars

More mortars


3 Comments leave one →
  1. christine permalink
    January 15, 2013 12:27 am

    Im just curious, how can you tell the difference between rock, bone fragments and wood when water screening?

    • matthewlaw permalink*
      January 16, 2013 4:42 pm

      Hi Christine,

      Thanks for writing. Usually you can tell by quick visual inspection, or by the feel of the find -rock usually (but not always!) feels heavier than a piece of bone or wood of the same size, but sometimes this is more difficult. Burning can affect wood or bone quite a lot – in particular at high temperature bone can turn white becoming what anthropologists and zooarchaeologists (who study animal bones) call calcined. Generally, you can still see telltale structures if you look at wood or bone through a magnifying glass or low-powered microscope though (take a look at this picture of an engraving on a piece of bone – you can see even the smooth outer surface of bone is quite porous

    • ). At even higher magnification, the differences become very obvious. Finally, if all else fails, you can check the chemical composition of finds using a process called X-Ray Fluorescence (XRF).

      I hope that’s some help


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