the diversity of these trees present a good record of past horticultural practices. The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales. The wall of the Cordeaux Dam is the longest of all the dams constructed in the Upper Nepean Catchment Area. Cordeaux Dam is one of three dams in NSW which incorporate extensive inter War Egyptian architectural detailing. Cordeaux Dam is one of two extant dams in NSW which incorporate pedestrian and vehicular entry pavilions to the crest wall. The crest and valve houses and inlet works retain original ironwork and machinery such as roller gates, penstocks and penstock opening sysyem which represent a substantial repository of water supply delivery technology for the era in NSW. The dam incorporates the first instance of multiple level water discharges and valve houses, and emergency roller gates in NSW. The ensemble of plant buildings either associated with the construction or completion of the dam, such as weatherboard machine shed (adapted to double garage) and the corrugated iron blacksmiths, are unique in situ examples within the broader context of the four Metropolitan Dams. The dam incorporates cyclopean masonry which is a construction technique unique to the Metropolitan Dams in Australia. The dam incorporates the first instance of internal inspection galleries and connecting pipework and V notch weirs in a dam in NSW. The place is important in demonstrating the principal characteristics of a class of cultural or natural places/environments in New South Wales. Cordeaux Dam is representative of a type of dam (cyclopean masonry gravity dam) constructed in NSW by the Department of Public Works during the first half of the twentieth century. Key representative attributes of the dam design and construction include the use of cyclopean masonry bedded in sandstone concrete, use of blue metal concrete in facing the upstream face, the use of sandstone concrete in facing the downstream wall, use of a spillway that is an extension of the gravity wall, upper and lower valve/crest houses attractively designed and finished to a high standard, the use of an array of upstream intakes to regulate the quality of water supply, the internal inspection galleries, the foundation grouting system, the contraction joints, and the internal drainage system. The upgrading of the valves within the dam wall and ancillary monitoring and operating equipment is representative of modern-day safe operating practice. The construction technologies used