St. Mary's Islands, also known as Coconut Island and Thonsepar, are a set of four small islands in the Arabian Sea off the coast of Malpe in Udupi. They are known for their distinctive geological formation of columnar basaltic lava. Scientific studies indicate that the basalt of the St. Mary's Islands was formed by sub-aerial subvolcanic activity, because at that time Madagascar was attached to India. The rifting of Madagascar took place around 88 Mya.  The islands form one of the four geological monuments in Karnataka state, one of the 26 Geological Monuments of India declared by the Geological Survey of India in 2001. The monument is considered an important site for "Geo Tourism".
According to folk legend, in the year 1498, Vasco da Gama landed at St. Mary's Islands on his journey from Portugal, fixed a cross on the island and named one of these islands, O Padrão de Santa Maria, as a dedication to Mother Mary, before proceeding to Kozhikode in Kerala. It is from this name that the islands got their current name.