The range is around twenty miles (thirty kilometres) in length, and runs southwest from Edinburgh towards Biggar and the upper Clydesdale.

'Muir', in Pentlandmure, describes common grazings where the farm's livestock would be pastured in summer; and gradually the name was linked more specifically with the slopes of the nearby hills (perhaps Allermuir, Woodhouselee or Castlelaw).

The oldest rocks are a sequence of Silurian mudstones, siltstones and sandstones collected together as the North Esk Group.

The Kinnesswood sandstones together with rocks of the Ballaggan Formation, which form the lower ground immediately northwest of the Pentlands, constitute the early Carboniferous age Inverclyde Group.

In the southern part of the hills is Little Sparta, the garden of the late artist and poet Ian Hamilton Finlay.

[7] About 20 m (66 ft) into Glencorse Reservoir lie the submerged ruins of the chapel of St Katherine's in the Hope.

According to the story, King Robert the Bruce staked the Pentland Estate against the life of Sir William St Clair, with the outcome of the hunt of a white deer by the knight and his two hounds, 'Help' and 'Hold', being the deciding factor.

The dogs managed to bring down the deer, and in gratitude, and to mark the spot, Sir William had a chapel built in the glen.

The incident is commemorated by the "Covenanter's Grave", a cairn after which one of the drove roads across the hills is known (OS Grid Reference NT078521).

[8][9] In Greyfriars Bobby, Bobby comes from (and later revisits) the Pentland Hills, whilst in Mary Shelley's novel Frankenstein, Frankenstein's friend Henri Clerval is said to have been filled with 'cheerfulness and admiration' when he visited the Pentland Hills while heading further north (Chapter 19).