Montana is a U.S. state in the Pacific Northwest and Great Plains regions of the United States. The central and western third of the state have numerous mountain ranges (approximately 77 named) of the northern Rocky Mountains; thus the state's name, derived from the Spanish word monta?a ("mountain"). The state nickname is the "Treasure State." Other nicknames include "Land of Shining Mountains", "Big Sky Country", and the slogan "the last best place". The state ranks fourth in size but has a relatively low population (with only six states having fewer people) and consequently a very low population density. The economy is primarily based on agriculture and significant lumber and mineral extraction. [citation needed] Tourism is also important to the economy with millions of visitors a year to Glacier National Park, the Battle of Little Bighorn site, and three of the five entrances to Yellowstone National Park.