This state historical marker about the interesting rock formations to be seen at this location is located along the I-80 frontage road in Buford WY.
This historical marker reads as follows:
"THE GANGPLANK
[inset topo map of the gangplank formation]
The granite rocks to the west are more than a billion years old (Pre-Cambrian in age). The sedimentary rocks to the east are some 10 million years old (Late Miocene in age). After the mountains were elevated, some 20,000 feet of rocks were eroded from their crest. Later the younger sedimentary rocks were deposited against the flank of the range.
The time between the formation of the granite to the west and the deposition of the onlapping sediments to the east is measured in terms of more than ten hundred million years. You are now standing on the gangplank.
The Wyoming State Archives and Historical Commission
and Wyoming State Historical Society"
From the Cowboy Country website: (
visit link)
"If this were a Wyoming geography class, we would have to note what geologists like to term, "The Gangplank" (El Tablon, or "The Plank"). It literally put Wyoming on the map.
As the easiest route from the Great Plains into the mountains, it is seen from Interstate 25. Interstate 80 and the Union Pacific Railroad cross the plains from Cheyenne to Laramie, on a rising plateau, to an escalating ramp that narrows into a "gangplank".
We still travel on a strip only 100 yards wide in some stretches. It's between the Laramie range and the Bighorn Mountains, and while "The Gangplank" made modern Wyoming, a case could even be made that without it, there would be no Wyoming.
There was no better latitude for coast to coast passing - for the Union Pacific, and the later Lincoln Highway. There certainly would have been no boom in the boomtown of Cheyenne. Maybe the plains city would never have been on the map.
It was the same historical route of the Oregon Trail, the Mormon Trail, and the Pony Express.
Just about the whole populace of Denver was furious at the news of how far south of the nation's tracks they would be. Well, Colorado just didn't have a "Gangplank."
Class dismissed."