10 most difficult ge­og­ra­phy of the United States riddles

White Sands, having 442 total square kilometers of dune fields, is the world's largest surface deposit of gypsum. Unlike other desert sands, it is cool to the touch, due to the high rate of evaporation of surface moisture and the fact that the sands reflect, rather than absorb, the sun's rays.

Yukon, having 1,979 mil (3,185 km), is just 223 miles shorter than Mississippi. Despite its length, there are only four vehicles-carrying bridges across the river.

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 4 most populous states are California (38M), Texas (26M), New York (19M) and Florida (19M).

Such large and rocky mountains are found only on the west of the North America. This is a photo of Mount Rainier over Tacoma, Washington, USA.

The easily recognizable Long Island extends 118 miles (190 km) eastward from New York Harbor. It is both the longest and the largest island in the contiguous United States.

The states of Maryland and Virginia each donated land to form the federal district with Washington.

Located on the Niagara River, which drains Lake Erie into Lake Ontario, the combined falls form the highest flow rate of any waterfall in the world.

The term Silicon Valley first appeared in the Electronic News newspaper in 1971. In 2006, Silicon Valley had 225,300 high-tech jobs.

The Missouri River is the longest river in North America. Having 2,341 mi (3,768 km), it is longer than the Mississippi (2,202 mi 3,544 km). When combined with the lower Mississippi River, it forms the world's third longest river system, after the Nile and Amazon.