Pastscape contains a detailed description. Summary:
The earthwork remains of an Iron Age promontory fort or hillfort and annexe. The headland of Bolt Tail is occupied by an Iron Age promontory fort of about 4.9. hectares, defended by a rampart 274 metres long and up to 4.6 metres high, with indications of a stone facing wall up to 4 feet high on its outer eastern side. The well-marked inturned entrance is approached by a hollow-way and guarded on the north by an arc-like outwork of stone, with a mound some 13 feet high by 53 feet long.
The hollow-way from the gate leads to a minor fortification on lower ground, where a small promontory facing north to Bigbury Bay is cut off by line of rampart running north-west to south-east, and about 2.7 metres high.
There is an entrance near the cliff-edge on the north-west. This camp seems to have been an annexe for the larger fort, sited to guard a fresh-water supply and observe Hope Cove below.Scheduled.