The Columbretes Islands (, or Els Columbrets (), are a group of small uninhabited islets of volcanic origin, in the Mediterranean Sea, off Orpesa. Administratively they belong to Castellón de la Plana in the Valencian Community. The main islets are Illa Grossa, La Ferrera, La Foradada and El Carallot. The total emerged area of all four is around and the highest point is above sea level. Illa Grossa, by far the largest, is the northernmost island of the group. It stands in the place of an ancient crater and shows a distinctive semi-circular pattern. There are no buildings on it, except for a 19th-century lighthouse, a jetty and the staff quarters used by the biologists working in the wildlife reserve. Geology The cone forming the Columbrete Grande was formed during four volcanic episodes from 1.0 to 0.3 million years ago. It consists of alkaline magmatism associated with the opening (rifting) of the Valencia Trough. Volcanism in other areas of the Valencia Trough coast dates between 10 million years and the present and they show a transition from calc-alkaline to alkaline signature. History These islands were known by Greeks and Romans from ancient times. Writers such as Strabo or Pliny the Elder cited the astonishing number of snakes inhabiting them. The names Ophiusa and Colubraria by which they were named (meaning serpent in Greek and Latin, respectively) refer to that fact. The islands owe their present name to "Coluber", the Latin word for "snake". After a lighthouse was built on Illa Grossa in the mid-19th century, a few people were settled on it. The small community looked after maintenance of the lighthouse and helped to deter smugglers who used the islets as a refuge. Farm animals including pigs were introduced. This, combined with aggressive practices such as the burning of the original bushy vegetation of the lighthouse island (partly for agricultural uses and also to deliberately deprive the numerous endemic snub-nosed vipers of their natural habitat), caused the snakes to become extinct by the end of the 19th century. The only testimony of their past abundance that remains today is a stuffed viper from the Columbretes in Madrid's Natural Science Museum. Island groups All islets and skerries are separated into four groups, all of them related to their position to one another: The islands in bold are the largest and most important ones of each group. The islands highlighted in cyan