Ulva's interior is moorland, while the spectacular geological formations of the south coast, have been somewhat overshadowed by those of its neighbour Staffa. Nonetheless, they are still renowned in their own right. Around 60 million years ago, the region was volcanically active, with Ben More on Mull being the remnant of a volcano, and it was in this period that the famous rock formations of Staffa and the basaltic columns of "The Castles" on Ulva came into being. The lava flows are known as the "Staffa Magma Type member" and can also be seen on Mull at Carsaig, Ardtum, and near Tobermory on its east coast. They are particularly rich in silica. These were formed when the cooling surface of the mass of hot lava cracked in a hexagonal pattern in a similar way to drying mud cracking as it shrinks, and these cracks gradually extended down into the mass of lava as it cooled and shrank to form the columns which were subsequently exposed by erosion.