Here, let us take a look at the Geography of United States. note 1: world's third-largest country by size (after Russia and Canada) and by population (after China and India); Mt. McKinley is the highest point (6,190 m; 20,308 ft) in North America, and Death Valley is the lowest point (-86 m; -282 ft)

note 2: the western US coast and the southern coast of Alaska lie along the Ring of Fire, which is a belt bordering the Pacific Ocean that contains about 75% of the world's volcanoes and up to 90% of the world's earthquakes

note 3: the Aleutian Islands are a chain of volcanic islands that divide the Bering Sea (north) from the main Pacific Ocean (south); they extend about 1,800 km (1,118 mi) westward from the Alaskan Peninsula; the archipelago consists of 14 larger islands, 55 smaller islands, and hundreds of islets; there are 41 active volcanoes on the islands, which together form a large northern section of the Ring of Fire

note 4: Mammoth Cave, in west-central Kentucky, is the world's longest known cave system with more than 650 km (405 miles) of surveyed passageways, which is nearly twice as long as the second-longest cave system, the Sac Actun underwater cave in Mexico (see "Geography - note" under Mexico)

note 5: Kazumura Cave on the island of Hawaii is the world's longest and deepest lava-tube cave; it has been surveyed at 66 km (41 mi) long and 1,102 m (3,614 ft) deep

note 6: Bracken Cave outside San Antonio, Texas is the world's largest bat cave and the summer home to the largest colony of bats in the world; an estimated 20 million Mexican free-tailed bats roost in the cave from March to October, making it the world's largest known concentration of mammals. Mother's mean age at first birth is N/A , whereas, the Maternal mortality ratio is N/A.