Most of the Wharfe valley, including where Ilkley is today, was an inhospitable swamp. The high ground was inhabited by hunter- gatherers, who lived near the vast woodlands, which covered most of the uplands of Britain thousands of years ago, providing an abundant food source for both humans and animals. Traces of prehistoric activity are found in the forms of flint arrowheads or microliths, which date from the Mesolithic period (11.000-9.000 BC). These artefacts were found on the surface or at various depths across Ilkley and Rombalds moor.
Over 250 rock carvings have been found within this area, and some experts believe that there may be more buried under the peaty soil. The rock carvings are found on cliff faces, especially near Cow and Calf rocks, and also on the boulders around the area of Green Crag Slack (Map Ref: SE1340). The local rock is known as Millstone Grit, a brownish-grey rough soft stone imbedded with quartz fragments.