Caxias is a Martian impact crater, approximately 25 kilometers in diameter. According to a surface age map of Mars based on US Geological Survey data, the area around Caxias is from the Noachian or Hesperian epoch, which places the area's age at 3.8 to 1.8 billion years. The crater is about 7,400 meters in elevation above zero altitude on its floor, and averages about 8,000 meters above zero altitude on its rim; it is therefore about 600 meters in depth. (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.