McKean refers to Auchans as being amongst Scotland's principal châteaux which he defines as the dwelling of the owner of a great property, a large and beautiful pleasure house in the countryside,[4] and records that James Wallace added the fashionable square stair-tower in the re-entrant angle,[5] with its viewing platform and broken pediments in 1644.

[8] The original house, with its high gables, had three principal storeys; the basement was vaulted and a stair-tower was situated externally, central to the South side.

A new wing, three storeys and a garret in height, was at a later date added at the West end of the North wall, and a stair-tower, with a Renaissance-style doorway, was built, still visible in the present ruins.

The now greatly ruined castle stands in its woodland policies amidst a series of stone-walled parks, the walls of which are mainly in a state of collapse.

[15] A vast number of valuable Eglinton family papers were discovered in one of the apartments in the 1880s, rescued as the building was in a terminal state of decay.

In 1875 this garden was still under cultivation and in the orchard had stood the parent tree of the famous Auchans pear, the first of its kind in the county, brought in from France (or Norway)[18] at an early date, said to be during the reign of Mary, Queen of Scots.

The mid-19th century OS maps show a complex of out-buildings and a dwelling called Old Auchans, situated above the castle and with Parkthorn farm nearby; it had views of what is now the quarry.

[22] Opposite Dundonald Castle is a high and precipitous bank, wooded, which until the 1820s formed part of the boundary of the Auchans deer park.

[24] Colonel James Wallace was the last of that family to occupy the castle;[25] he was an active supporter of the Solemn league and Covenant and led the rising at Pentland in November 1666.

In 1640 the estate passed to his relative Sir William Cochrane of Cowdon, an arrangement carried out prior to Colonel Wallace's participation in the insurrection.

[26] Sir William also suffered during the Civil War, but after the restoration of the monarchy he was created Earl of Dundonald in 1669 for his services to the Crown.

[1] In 1876, it is recorded that one of the side angles had the date of 1644 and another of 1667; a marriage stone had the initials WCD (William Cochrane of Dundonald) and ES (Eupheme Scott) also occurred in two places.

of Whitmuir Hall near Selkirk has a memorial plaque, giving the fact that he was Factor to Lady Susanna Montgomery at Auchans and died in 1836, aged 61.

[30] In 1846 the property was owned by Lady Mary Montgomerie, by whose servants it was chiefly inhabited and it was becoming ruinous, with parts untenanted and locked up.

[10][31] The structure was altered quite considerably to accommodate the workmen and some features, such as ornate marble fireplaces, were removed and taken to Auchans House, now demolished.

[32] In 1892, following the death of Archibald William, the 14th Earl of Eglinton, his daughter Lady Sofia Constance Montgomerie inherited the Auchans estate that comprised the house and policies together with the farms of Bogside, Broomhill, Clevance, Crooks, Girtrig, Guilliland, Highlees, Kilnford, Laurieston, Parkthorn and Ploughland.

[38] Susanna is remembered for eccentrically taming a number of rats at Auchans to come for food at her table when she tapped on an oak wall panel and opened a small door.

[40] Recorded names for Auchans are Achinynche (15th Century), Auchinche (1512), Achans, Achnes, possibly derived from the Gaelic 'Achaidhean' - 'tilled fields'.

The new mansion of Auchans was built in the style of an Italian villa, with projecting glazed porch, giving access to the hall and main staircase.

The land around the house was richly wooded, and this character was carefully preserved, so that from whatever side the dwelling was approached it was against a background of woodland.

The carriage-drive was bordered for a considerable distance with a symmetrical parterre of flowers, and an extensive conservatory formed an exterior wing to the mansion-house.

An urn, containing fragments of human bones, was found near Auchans Castle by a workman who was digging in a small mound of gravel.

Ash, oak and sycamore are also abundant; much of the policies are composed of derelict-coppiced-type growth from trees felled in the Second World War.

Wetland habitats are also present, with springs, an old reservoir near Collennan and a very eutrophic water body, Merklands Loch, all contributing to the high biodiversity of the site.