I live in Denver Colorado. So your semi-humble Metric Maven is constantly bombarded by the phrase: “Mile High City,” and the number 5280. Even the Denver Nerd Nite logo is a pseudo-element with 5280. The mascot of the Denver Broncos is named Miles. Clearly, it must have been apparently early on that my fair (now getting rather overcrowded) city had a special and obvious geographical significance of existing at one mile above sea level to earn that nickname. The true story is more complicated. Denver is fortunate that it has its own “historian at large,” Phil Goodstein. He has written many books about the history of Denver, and its component neighborhoods. In his book Robert Speer’s Denver 1904-1920,  he addresses how Denver obtained its nickname—The Mile High City. It is reproduced below:
Among other things, the Convention League wanted Denver to dump its nickname as the “Queen City of the Plains,” or “Queen City of Mountain and Plain.” Both appellations had been used since the 1880s. Other metropolises called themselves the “Queen City” in the late 19th century, including Cincinnati, Seattle, and Buffalo. Against this, the Convention League urged labeling Denver the “City of Hospitality,” advertising to one and all that it was a pleasant place to come and spend money. The Denver Times suggested calling Denver the “City of Homes” to advertise how many residents owned their own abodes.
These proposals never amounted to much. Already in the late 1880s and early 1890s, Denver had sometimes described itself as the “Garden City of the Plains.” Prior to Speer’s taking office on June 1, 1904, some simply sought to call Denver “The City Beautiful.” Such was the slogan of “Seeing Denver,” special tourist excursion streetcars operating from the Brown Palace. The title dropped away as “city beautiful” became more generic than a distinctive moniker. During the 1910s when Denver was starting to develop its mountain parks system, the Real Estate Exchange urged promoting the town as at the “Foot of the Rockies.” The Colorado Publicity League endorsed the trademarked slogan, “Denver: Front Door of the West.” Others urged labeling the metropolis the “City of Sunshine,” and the “Top of the World,” the community where the mountains met the plains. Shortly after World War I, Denver embraced a new identity as the “Mile High City.”
Originally, locals paid little attention to the town’s altitude. Nineteenth-century reports listed its elevation as approximately 5,170 at 15th Street and the Platte River to about 5300 feet above sea level. Around the beginning of the 20th century, residents began to stress Denver’s mile high status. Tramway [A local tram company] denoted this at its cable powerhouse at Colfax and Broadway. The red sandstone cornerstone of the 1888 edifice read “one mile above sea level.” It quickly came out that engineers had misjudged the altitude. The company responded by placing a sign on the second story telling passersby the elevation. On occasion, other businesses referred to themselves as “mile high” this or that. Nonetheless, not until the second decade of the 20th century did Denver begin to have the self-mage as the Mile High City. After the “City of Hospitality” failed to take root, the “Mile High” moniker burst forth. (When the city demolished the Tramway powerhouse in 1913 to make way for the Civic Center, it gave the cornerstone to
the Chamber of Commerce which placed it in the dining room of its Temple of Commerce at 1726 Champa Street.)
Prior to World War I, there had been no consensus about the town’s altitude. Even
when Denver Municipal Facts promoted Denver as the Mile High City in 1911, it listed the town’s altitude as 5284 feet above sea level. A comparable tourist promotion brochure issued in 1916 had Denver at 5,190 feet. In 1913 a civil engineering report listed the extremes of the city’s height as between 5,126 and 5,482 feet above sea level. Nor have geologists always agreed about the city’s exact elevation.
This came out at the Capitol. Mile High champions observed the seat of the government was exactly one mile above sea level. So one and all would know and
appreciate this, the state placed a brass plate on the west steps of the building in 1909, declaring as much. During the first half of the 20th century, the city installed brass markers around town to pinpoint locations a mile above seal level. As was the case at the Capitol, they disappeared.
After vandals had stolen the fourth such medallion from the Capitol steps in 1947, the building’s longtime superintendent James Merrick, ordered workers to engrave a step on the Capitol, stating one standing atop it was a mile above the ocean. In 1969, college students, seeking to confirm the altitude, discovered the step was only about 5,278 feet above sea level. (Already in 1913, an East High School Physics teacher had asserted it was off by four inches.) In the wake of the 1969 report, the state placed a new Mile High emblem a few steps above the engraved inscription. A 1988 modification of the definition of sea level led to a new survey in 2002, which challenged the accuracy of the second marker. This lead to the installation of a third emblem on the west steps of the Capitol in September 2003.
This explains why John Shafroth (1854-1922) never seemed to have any mention of Denver’s mile high status appear in his bid for the metric system in Congress. The name had not been minted and marketed yet. No one in the Congressional hearings on metric would be familiar with Denver as the “Mile High City,” and throw it out as a bit of
rhetorical hectoring as they opposed the logical measurement system. David Baron in his interesting book American Eclipse refers to Denver as The Queen City as it prepared for the arrival of the total solar eclipse of 1878.
What is not mentioned is that the tokens marking one mile, are on the State Capitol Building, not the city and county building, The city government of Denver is clearly not one mile above sea level. It seems like using the building that is supposed to represent the entire state is cheating, and leaves out the majority of Colorado’s population. Below is an elevation map of the Denver City and County Building:
Google reports it as 5243 feet or about 11 meters shy of a mile. Below is the elevation reported for the Statehouse for reference:
As I’ve pointed out, different countries have different definitions of sea level, so no matter where we chose our location for a mile above sea level, that will only be for the US definition of sea level. Once the world considers using the center of our planet as a reference, then the Mile High City is no longer a mile high.
Clearly, there is only one fair way to resolve this situation, the entire state of Colorado is the only US state which is 1 Kilometer above sea level. We should change the signs at our Colorado state borders to read “Welcome to Colorful Colorado — The Kilometer High State.”
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 Goodstein, Phil, Robert Speer’s Denver 1904-1920, Denver New Social Publications 2004 pp 108-110