Dinorwic is a Martian impact crater, approximately 56 kilometers in diameter. It is located on the planet Mars at 30.4°S, 101.6°W, northeast of the crater Virrat and north of the crater Tugaske. To the northeast is the crater Caxias, and farther north is the crater Llanesco. (wikipedia entry)
A crater is a circular depression likely created by an impact event. On Mars large craters are named after deceased scientists, writers and others who have contributed to the lore of Mars. Small creaters (less than 60km) are named after small towns and villages.