The moai in the park are of varying height from 2 to 20 metres (6 to 65 ft). The volcanic rock formations quarried for sculpting are a distinctive yellow-brown volcanic tuff found only at the Ranu Raraku on the southeast side of the island. Some of the moai were also carved from red scoria. The ceremonial shrines where they are erected for offering worship are known as ""ahu"". Of impressive size and form, they are normally built close to the coast and parallel to it. Many unfinished moai are also found in the quarries. The production and transportation of the 887 statues are considered remarkable creative and physical feats. The moai have been under restoration since 1950. The period between 1837 and 1864 was a critical time when, for reasons that remain unknown, all the standing statues were toppled (probably during the tribal wars), although with little damage. Subsequently they were retrieved and returned to their original positions during the period of restoration with international assistance. The moai represented a clan's "most revered forebears who were believed to bestow ‘mana’ on living leaders". The park also has a few petroglyphs and paintings.