According to oral history, George Washington visited the canal diggings in 1792, and then again in 1794, while he was accompanying troops to suppress the Whiskey Rebellion in Western Pennsylvania.
1970
![Union Canal Tunnel](/sites/default/files/styles/landmark_node_/public/2018-03/Union_Canal_Tunnel_LebCo_PA_2.jpg?itok=i246vEbL)
![Theodore Roosevelt Dam](/sites/default/files/styles/landmark_node_/public/2018-03/8655562922_e48b3f5afb_o.jpg?itok=r1CX-FTy)
The first electric power generated by the Theodore Roosevelt Dam for commercial use was transmitted over a high-voltage line to Phoenix, where it was employed to operate the city's new streetcar system.
![Potowmack Canal and Locks](/sites/default/files/styles/landmark_node_/public/landmarks/images/Potowmack_Canal_and_Locks.jpg?itok=vI0ZqYFi)
These canals and locks are a part of the first extensive system of canal and river navigation works undertaken in the United States. The idea for the canal was proposed by George Washington, when, as an engineer, surveyor and military emissary for Virginia, he saw the need for a trade route west beyond the Allegheny Mountains. In order to do create this route, it was necessary to try to tame the Potomac River which was a wild, unruly stream which only the hardiest of rivermen ever attempted.
![Frankford Avenue Bridge](/sites/default/files/styles/landmark_node_/public/2018-03/1280px-Frankford-Avenue-Bridge.jpg?itok=ne2MqWrA)
"For 273 years, the little stone bridge that carries Frankford Ave. across Pennypack Creek has been doing its humble job with a minimum of attention..."
- Gerald McKelvey, The Philadelphia Inquirer, September 16, 1970
![Cornish - Windsor Covered Bridge](/sites/default/files/styles/landmark_node_/public/landmarks/images/Cornish_-_Windsor_Covered_Bridge.jpg?itok=Hnw6Sufo)
The Cornish-Windsor Covered Bridge is the longest wooden bridge in the United States and the longest two-span, covered bridge in the world. It is also a classic example of wooden bridge-building in 19th-century America. With copious supplies of timber at hand and a generous reserve of carpentry skills available, bridge builders in early America quickly discarded the masonry arches prevalent in the Old World. Instead, they opted for a revival of timber-truss designs dating from 14th century Europe.
![Bridgeport Covered Bridge](/sites/default/files/styles/landmark_node_/public/landmarks/images/Bridgeport_Covered_Bridge.jpg?itok=vYNDPG3N)
A product of the Northern California Gold Rush, the Bridgeport Covered Bridge is believed to be the longest, single-span, wooden covered bridge in the United States. Crossing the south fork of the Yuba River at a span of 233 feet, the bridge was built by the Virginia City Turnpike Company as part of a 14-mile toll road authorized by the California state legislature. The toll road was an essential link connecting Virginia City, Nevada, and the silver-producing Comstock Lode with the centers of California commerce.
![Ascutney Mill Dam](/sites/default/files/styles/landmark_node_/public/landmarks/images/Ascutney_Mill_Dam.jpg?itok=QgCwNcJd)
Ithamar A. Beard, an engineer of some prominence in New England, surveyed the mill brook and selected the best site for a storage dam. Contractor Simeon Cobb, knowledgeable of contemporary civil engineering practices, made major changes to the dam's original design, converting the linear dam into a gentle arch.
Innovations
![Ascutney Mill Dam](/sites/default/files/styles/thumbnail/public/landmarks/images/Ascutney_Mill_Dam.jpg?itok=FfQYbFk_)
Ithamar A. Beard, an engineer of some prominence in New England, surveyed the mill brook and selected the best site for a storage dam. Contractor Simeon Cobb, knowledgeable of contemporary civil engineering practices, made major changes to the dam's original design, converting the linear dam…
Read More![Bridgeport Covered Bridge](/sites/default/files/styles/thumbnail/public/landmarks/images/Bridgeport_Covered_Bridge.jpg?itok=4hNdPevE)
A product of the Northern California Gold Rush, the Bridgeport Covered Bridge is believed to be the longest, single-span, wooden covered bridge in the United States. Crossing the south fork of the Yuba River at a span of 233 feet, the bridge was built by the Virginia City Turnpike Company as…
Read More![Cornish - Windsor Covered Bridge](/sites/default/files/styles/thumbnail/public/landmarks/images/Cornish_-_Windsor_Covered_Bridge.jpg?itok=5jIO1PFI)
The Cornish-Windsor Covered Bridge is the longest wooden bridge in the United States and the longest two-span, covered bridge in the world. It is also a classic example of wooden bridge-building in 19th-century America. With copious supplies of timber at hand and a generous reserve of carpentry…
Read More![Frankford Avenue Bridge](/sites/default/files/styles/thumbnail/public/2018-03/1280px-Frankford-Avenue-Bridge.jpg?itok=0VtLUxxp)
"For 273 years, the little stone bridge that carries Frankford Ave. across Pennypack Creek has been doing its humble job with a minimum of attention..."
- Gerald McKelvey, The Philadelphia Inquirer, September 16, 1970
Built more than a century before the reign of Napoleon,…
Read More![Potowmack Canal and Locks](/sites/default/files/styles/thumbnail/public/landmarks/images/Potowmack_Canal_and_Locks.jpg?itok=kIgHuhE-)
These canals and locks are a part of the first extensive system of canal and river navigation works undertaken in the United States. The idea for the canal was proposed by George Washington, when, as an engineer, surveyor and military emissary for Virginia, he saw the need for a trade route west…
Read More![Theodore Roosevelt Dam](/sites/default/files/styles/thumbnail/public/2018-03/8655562922_e48b3f5afb_o.jpg?itok=16DjwMr2)
The first electric power generated by the Theodore Roosevelt Dam for commercial use was transmitted over a high-voltage line to Phoenix, where it was employed to operate the city's new streetcar system.
The Salt River Project, including the Theodore Roosevelt Dam, was the first major…
Read More![Union Canal Tunnel](/sites/default/files/styles/thumbnail/public/2018-03/Union_Canal_Tunnel_LebCo_PA_2.jpg?itok=cYnRsmv9)
According to oral history, George Washington visited the canal diggings in 1792, and then again in 1794, while he was accompanying troops to suppress the Whiskey Rebellion in Western Pennsylvania.
The Union Canal Tunnel was a crucial structure allowing the connection of the eastern and…
Read More