Cairn I at Pen Trumau is a stone cairn, 20m in diameter and up to 2m high, on the edge of a natural terrace below Pen Trumau. Turf and bilberries covered the edges but most of the cairn was clear of vegetation when recorded in November 2007. The centre of the cairn was disturbed.

Associated sites:
NPRN 267019 is a shelter built on the east side of the cairn. NPRNs 267020 & 267021 are two modern cairns on the top of the cairn. NPRN 267022 on the south side is a small ring cairn. NPRN 267023 beyond that is an elongated low stony mound.

Reference: RCAHMW , 1997 , An Inventory of the Ancient Monuments in Brecknock (Brycheiniog); The Prehistoric and Roman Monuments, Part i .

J.J.Hall, Trysor, 4 November 2007