The Salton Sea in California and is a great inland sea. With no discharge for its water, the lake gets saltier every year. The Salton Sea was created in the early 20th century when a dike broke, allowing water to flow in from the Colorado River. It took almost two years to stop the Colorado River from changing its course through the Salton Sea.

Pittsburgh is represented by number 4 on the map. There are many factories and steel mills in Pittsburgh. It is located where the Allegheny and Monongahela Rivers flow together and form the Ohio River.

The Midwest was the center of manufacturing in the United States beginning in the late 19th century and extending well into the 20th century. Good transportation links, availability of natural resources, and a good supply of fuel to power the factories helped to expand industry and make the United States an economic power.

In 1836, the Georgia General Assembly voted to build the Western and Atlantic Railroad as a trade route to the Midwest. In the 1840s, the chief engineer of the railroad suggested renaming the area Atlantica-Pacifica, which was shortened to Atlanta. Today, the city's airport is the busiest in the world, and its financial area includes the home office of SunTrust Banks and the district headquarters of the Federal Reserve System.

Which Pacific Coast city has been through several boom-and-bust periods in its history, starting with a lumber boom in its early years, followed by booms in gold mining, shipbuilding, and aviation? Los Angeles, Seattle, San Francisco, or San Diego

Seattle's boom-and-bust cycles are common for cities its size. The most recent boom was due to technology companies and biomedical corporations, although the local economy has cooled since the end of the dot-com boom of the late 1990s.

Kitty Hawk is on the Atlantic coast in North Carolina. The area was chosen for an early test flight because the area is very windy and has soft sand that could act as a cushion in the event of a crash.

The Grand Canyon is located in northern Arizona and is shown as the number 2. It is more than one mile deep and nearly 300 miles long. The Colorado River flows through it.

The Great Plains lie in the middle of the United States. Good soil makes the area good for farming. The farms in the region produce enough crops for use in the United States as well as for export to other countries.

The steel industry was important in the growth of the railroads across the country. Without cheap steel to create thousands of miles of steel rails, transportation over land would be too expensive for economic growth.

In Denver's early days, gold and silver booms played an important role in the city's economic success. Mining remains important in Denver, along with telecommunications and real estate

The Columbia River, which begins in Canada, was the river that brought Lewis and Clark to the Pacific Ocean. The river is more than 1200 miles long and is important for its dams and hydroelectric plants.

The Spanish explored the Colorado River, which begins in the state of Colorado, flows through the Grand Canyon, and ends at the Gulf of California. It was called the Colorado because of the red sediment it carried in its water.

Lake Huron is number 3 on the map. It is connected to Lake Michigan at the Straits of Mackinac and both lakes have the same water level. Huron is the second largest of the lakes in terms of surface area. Manitoulin Island in Lake Huron is the world[?]s largest island in a lake.

One of Pittsburgh's earliest industries was building boats for settlers to enter the Ohio Country. The city began to produce steel in 1875 when Andrew Carnegie founded the J. Edgar Thomson Steel Works, which evolved into the Carnegie Steel Company. In 1901, U.S. Steel Corporation was formed. Within 10 years, Pittsburgh was producing between one-third and half of the nation's steel. That was made possible by a population that had grown to half a million.

On the map, the symbol for cattle is found in the states of Texas, Arizona, and New Mexico. These states are in the Southwest.

The Mojave Desert is represented by the number 2 on the map. It covers more than 25,000 square miles. The city of Las Vegas, Nevada, is the largest city in the desert.

The number 3 represents Pearl Harbor on the Hawaiian island of Oahu. It is near the city of Honolulu and has been used as a naval base by the U.S. since the 1800s. The attack by the Japanese in December 1941 caused the United States to join World War II.

The Battle of Gettysburg, fought near the town of Gettysburg in Pennsylvania, was a turning point in the American Civil War. The victory by the Northern Army pushed General Lee and the Southern troops south and out of the North's territory. The South lost support in Europe, and 21 months later, the war was over.

With the growth of the railroad, it became easier and cheaper to move raw materials and natural resources to markets in the east.

Power was needed to produce large numbers of textiles and fabrics. In the days before electricity, waterpower was used. Factories were built along New England's many rivers and streams to run the looms and mills. The steady supply of workers from area towns made the textile industry very profitable.

The Transcontinental Railroad shortened travel times between the East and the Pacific Ocean. Gold and other resources could quickly and cheaply be shipped to the East and manufactured goods could be shipped to the West. The railroads were an important part of the expansion of industry in the U.S. during the late 19th century.

Lake Michigan, bordered by the states of Michigan, Wisconsin, Illinois, and Indiana, is the only one of the five Great Lakes that is not part of Canada. Lake Michigan is the second largest of the lakes in volume of water. Two of its principal cities are Chicago and Green Bay.

The Great Lakes are an important transportation route from the middle of North America to the Atlantic Ocean by way of the St. Lawrence Seaway. Because the locks are too small for today[?]s oceangoing ships, much of the transportation is intra-lake (lake to lake) instead of continuing on to the Atlantic Ocean. (Locks are sections of a waterway closed off with gates.)

The steam engine made it possible for factories to be located away from fast moving rivers. With a supply of water and a fuel source such as wood or coal, factories could be built and powered closer to natural resources. For example, before the Civil War, textile factories were located mainly in New England where there were plenty of rivers even though the cotton they used was grown in the South.

Iron ore was easily moved from deposits in northern Michigan through the locks on the Great Lakes and on to the steel mills in Pittsburgh and western Pennsylvania. By making it cheap to transport the raw material needed for steel, the locks helped fuel the steel industry and the building of America's railroads and skyscrapers.