The Whimble cairn does not appear to be discussed in the book, other than a mention that it`s there. The excavations were all carried out further east, on lower-lying ground.

The date given for the Hindwell enclosure is c2700BC.

You may be interested in this, too (about the enclosure):

There was no trace of an inner or outer bank. Of the post-holes for the palisade it says they were 0.8m in dia., 2m. deep with average gap between of 0.7m. The posts probably stood at least 6m. above the ground. 1,410 posts would have been needed, each weighing about 4.5 tonnes.

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