How Old are Clam Gardens?

Determining how long ago a clam garden wall was built can be tricky since rocks are not easily dated. Instead, archaeologists try to find once living materials, such as wood, charcoal, bone, and shell that are associated with the building of the rock wall. The radiocarbon dating method allows us to determine how long ago these organisms (trees, animals, shellfish) died. Our team has figured out that clam garden age can be determined by either dating “barnacle scars” (the place on the rock where the barnacles were attached) on rocks from within the garden wall, or by dating clams trapped at the base of the wall when the wall was initially built. In addition to radiocarbon dating, we are also experimenting with luminescence dating. This method measures the last time sediments within the clam garden terrace, or on the old beach below the garden, were exposed to sunlight. Based on our dating thus far, some clam gardens are at least 2,000 years old.

Photo: Nicole Smith.
Barnacle scars on boulder at base of clam garden wall. Photo: Nicole Smith.

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