The cliffs here display the typical rock types of the Old Red Sandstone sequence. Not all the sandstones are red, some may also be purple, green or grey.

The layers of rock were laid down by rivers that flowed on an ancient continent south situated of the Equator, on a hot plain crossed by braided river systems, and represent sediments deposited in river channels and on flood plains.

The rocks were formed during the Devonian Period and are around 400 million years old. They reached their present position through continental drift - the movements of the plates which make up the Earth's crust.

In the Devonian Period, vegetation cover on the land was limited to very small plants (typically consisting of a fine rootlet with a spore case at the top and no bigger than a pin). These plants were confined to the margins of the land and grew in environments similar to the salt marshes which exist in Sandy Haven Pill today.

In the south-eastern corner of the bay the rocks have been folded downwards (this type of fold is known as a syncline). A collision of continents that occurred around 290 million years ago caused the folding and faulting that affects the rocks of south Pembrokeshire.

Kilroom Bay is surrounded by a narrow strip of marine grassland where there is red sescue grass, and in rock crevices clumps of thrift, kidney vetch and sea campion, buck and sea plantain.

The bands of colours that you can see on the Old Red Sandstone rocks are layers of differently coloured lichens: orange, yellow and black. The black layer is black tar lichen, which people often think looks like oil. Following this is the intertidal zone. This overall effect is known as 'vertical zonation'.