Sandleford Warren was a warren ran by the Threarah. It was the home of Hazel, Fiver, Pipkin, Bigwig, Hawkbit, Dandelion, Blackberry, Silver, Acorn, Buckthorn, Speedwell, Bluebell, and Holly prior to its' destruction. A notice board, discovered by Hazel and Fiver makes Fiver nervous, his instinct telling him that the sign meant danger. The Warren's destruction was predicted by Fiver, who insisted that they all must leave as soon as they can. The Chief rabbit Threarah, refuses to hear Hazel or Fiver and punishes Bigwig for allowing them to even speak to him with such nonsense.
After it is destroyed, Holly finds the group on Watership Down and describes the horrors that the warren faced in its last day. Men came and poisoned the burrows and runs, shooting any rabbit who tried to run away. Many could not escape because the runs were blocked by dead bodies and he describes a boy putting the bodies on a stick, but is soon stopped from getting too grim by Hazel. It is not known exactly what happened to Threarah, and Holly expresses that he hoped the Chief died quickly.