USA

The stone was set by the joint U.S.-Spanish survey party on April 10, 1799.  Made of sandstone, it is roughly two feet high and eight inches thick. On the north side of the stone is the inscription "U.S. Lat. 31, 1799." On the south side is "Dominio de S.M. Carlos IV, Lat. 31, 1799."

The Wheeling Suspension Bridge was the first bridge to span the Ohio River. It was initially completed in 1849, but destroyed by a tornado five years later. The bridge was rebuilt in 1856. The replacement bridge has the same general appearance of the original structure; the massive towers, anchorage housings, and island approach are all the original stone masonry.

One of the first major efforts to increase farming and encourage habitation in the arid regions of the western United States, the Rio Grande Project was designed to provide reliable irrigation as well as resolve a dispute over water supply with the Republic of Mexico.  The project's centerpiece is Elephant Butte Dam, a concrete gravity structure 301 feet high and 1,674 feet wide. Elephant Butte Reservoir - with a surface area of 36,600 acres and a capacity of more than 2.2 million acre-feet - was the largest reservoir in the world at the time of its completion.

Established in 1935 as the Valparaiso Bombing and Gunnery Base, the base supported the U.S. Army Air Corps, the predecessor to the U.S. Air Force, as its primary facility for training new pilots in bombing and gunnery tactics. It also served as a test facility for aircraft, aircraft armament, air-delivered munitions and other aircraft systems. The base was renamed Eglin Field in 1937 in honor of Air Corps aviator Lt. Col. Frederick I. Eglin, who trained pilots during World War I, and who had recently died in an aircraft accident. After Congress created the U.S.

Edison's simple and unprecedented instrument allowed for the first time the permanent recording and reproduction of sound, especially the human voice. On December 6, 1877, Edison put tinfoil around the cylinder, turned the handle of the shaft and, shouting into one of the diaphragms, recorded a verse of Mary Had a Little Lamb "almost perfectly." From this machine evolved the phonographs and record industries of the world.

This dynamo, connected directly to a high-speed steam engine, was one of six that produced direct current at Thomas A. Edison's electric power station at 257 Pearl Street in New York City. The Pearl Street Station was the prototype for central station power generation. Edison set out in 1878 to provide an electrical distribution system to bring lighting into the home: His first filament lamp lit on October 21, 1879. With the help of Frances Upton and C.L. Clarke, Edison built his engine-driven dynamo for the 1881 Paris Electrical Exposition.

Operated by the Philadelphia Electric Company (PECO), now known as Exelon Corp., Eddystone Station Unit #1 is a 325 MW pulverized-coal-fired plant that pushed the technology of steam-electric generating plants. When built in 1960, engineers sought to make a more efficient plant using higher temperatures and pressures and larger machines. Previous experience at Philo 6 (Zanesville, Ohio, 1957) had demonstrated supercritical steam plants would work, so engineers pushed beyond that frontier to even larger machines and efficiencies.

In the decade following the Civil War, the Mississippi River began to lose its standing as the primary transport artery in the Midwest. Railroads were taking over, and Chicago was rapidly becoming the center of Midwestern commerce. The Eads Bridge was the first major railroad link over the Mississippi, constructed by the city of St. Louis in an attempt to maintain its dominance as a regional commercial hub.

The Durango-Silverton Narrow Gauge Branch of the Denver & Rio Grande Western Railroad extends from the town of Durango to the mining camp of Silverton. Built in 1882 through one of the most rugged mountain areas of the nation, its complexity remains a testament to the role civil engineering played in the development of the western United States. 

The tracks rise up the sheer, steep Animas Canyon, running along a rock ledge just wide enough to carry the train. The line is used today as a tourist attraction, carrying visitors through the picturesque San Juan Mountains.