Cookstown Sandstone is part of the Sherwood Sandstone Group. This was formed during the Triassic Period 248 to 206 Million years ago, the sediments were formed at a time when deserts and tropical oceans prevailed and the British Isles occupied the position of where Sudan is today. During this time flood events deposited sand and silt to produce the sandstones and mudstones seen today.
Cookstown Sandstone ranges in colour from pale pink to red and weathers by flaking, scaling and bedding-plane erosion. Thin section analysis shows Cookstown Sandstone to be more calcareous than Scrabo Sandstone which is also part of the Sherwood Sandstone Group.