The Swallows, Amazons and Ds Mining Company is the owner of the Golden Gulch copper claim on High Topps.
When they "stake" their claim in 1931 (PP21), Nancy writes "S.A.D. MINING COMPANY" until Roger asks "But why sad?". So the sign reads:
S.A.D.M.C. / THIS GULCH IS CLAIMED / JUMPERS BEWARE / BY ORDER S.A.D.M.C.
The idea of legally "Staking a Claim" comes from 19th century gold rushes in California, the Yukon, Australia and New Zealand; not from English law.
The claim was later developed in to a mine by Jim Turner, Timothy Stedding and Slater Bob.
The following summer, when Dick asks how they are getting on with the the mine, Timothy says Not so bad. We've cut into the vein at eleven places .... Dick is to help Timothy with the assays (PM2). When theo go for a Care-Free day an the mine, the entry was hidden now by huge piles of broken stones and there are shafls down from above (and) small grey piles of broken stone up on the hillside. When they go in, Dick notices that the cave was twice the size it had been (PM24).