The most difficult ge­og­ra­phy of Mexico riddles

Rio Grande is the fourth or fifth longest river system in North America, but it flows through arid and desert regions. The average discharge is just 82 m³/s (St Lawrence: 10100, Yukon: 6200, Colorado: 1200). It is also very variable, occasionally rising to over 10000 m³/s or dropping to 1 m³/s. During portions of 2001 and 2002 the mouth of the Rio Grande was blocked by a sandbar.

The cave near Naica, Mexico, was discovered in 2000 by miners. At that time, it was completely submerged. Today, the cave is accessible because the mining company's pumping operations keep it clear of water. Unfortunately, the crystals deteriorate in air, and soon may be lost.

A number of pre-Hispanic cities put Mexico in the first place in the Americas and sixth worldwide. There are 33 World Heritage Sites in Mexico, 21 in US, 19 in Brazil and 11 in Peru.

The fence on the US-Mexican border can be adjusted to remain on top of the ever shifting sand dunes. It is a special construction of narrow, 15 feet tall elements, that are movable vertically.

The Peninsula extends 1,247 kilometres (775 mi) and is divided between two Mexican States, Baja California and Baja California Sur.

The total population of Mexico is 112M. The second largest Spanish-speaking country is Colombia with 47M. For reference, the Spanish-speaking population of the United States is 35M.

The official name of Mexico is the United States of Mexico. Several other such countries existed in the past, including the United States of Brazil (1937-1967), United States of Colombia (1863-1886) and United States of Indonesia (1949-1950).