The geological deposits at this quarry were laid as a result of glaciation no more than 10000 to 12000 years ago. Glacier movements in Wales were confined to the major valleys which in this area involved the Teifi Valley Glacier. It is believed that within the confines of Cardigan Bay and North Pembrokeshire that both the Welsh Ice and the Irish Sea Ice met. The Irish Sea Ice had the effect of halting the movement of the Tiefi Valley Glacier. Consequently when the ice started to melt on land this resulted in the formation of several large lakes behind the Irish Sea Ice.

Within this area there were three such lakes of significance. Lake Ayron within the area of Aberaeron and Lampeter, Lake Teifi which covered the Teifi Valley down to Cardigan and Lake Nevern which is an overflow of Lake Teifi in the Newport area.

The Pantgwyn quarry lies in the overflow area between Lake Teifi and Lake Nevern and is unique in terms of the grades of sand and gravel found. The deposits contain coarser grain aggregates due to the presence of the larger gravel within. This is probably due to the overflow between Lake Teifi and Lake Nevern where the siltier deposits were washed away further into Lake Nevern as a result of the faster flowing waters between the lakes. This had the effect of leaving behind the larger lump gravel and coarse grain aggregates at this site with very little silt content.

The sand quality is of the highest order. Not only is it free from silt, clay and organic matter or other possible contaminants but it also passes the requirements needed for British Standards. The gravel complies with the material specification for Type 6C and Type 1 B of the Department of Transport Specification of Highway Works which means it is of sufficient quality to enable it to be used for a range of Civil Engineering uses.