In southern Colorado, US 85 gets no respect. But in northern Colorado, it's a different story. Weld County and several of its municipalities along US 85 embrace the route. In 2011, they collectively christened it the Centennial Highway:
The original bridge over Cottonwood Creek in this area was the 1887 stone arch bridge for the ATSF railroad. A parallel auto road was also built right along the west side of the RR. This became one of the most important early auto routes in Colorado, running north-south along the Front Range (in other words, a precursor to today's I-25). In fact it was designated "State Highway #1" in the 1920s. A new bridge for this road was built in 1923-24, just downstream (west) of the RR bridge. This is the same bridge that still stands today. It has long since been surrounded by the urban expanse of Colorado Springs, but back in 1924 this area was still quite rural. It was not yet a part of the Springs and the road was probably not yet referred to as Vincent Drive. This photo was taken from a vantage point on the stone arch bridge (now "New" Vincent Drive), looking west down Cottonwood Creek towards Pikes Peak. The 1924 bridge which carried "Old" Vincent Drive is visible just beyond the rec trail bridge in the foreground:
(Most recently updated 1/11/2020.) Today, Denver is served by seven different US routes: US 6, US 36, US 40, US 85, US 87, US 285, and US 287...
...but when the US highway system was first commissioned in late 1926, only three routes went through Denver. AASHO officials acknowledged the city's importance by placing it at the junction of a major north-south route (US 85, which ran from a Canadian port of entry almost to Mexico) and a transcontinental east-west route (US 40, which connected Atlantic City NJ to the San Francisco Bay Area):
Colorado is somewhat infamous for not signposting its US routes where they are concurrent with interstates. This is more than just signage policy: CDoT route logs actually divide US routes into segments, and these segments are discontinuous in cases where the US route shares pavement with an interstate. So in a sense, CDoT considers US routes to be non-existent wherever their implied route is on an interstate. This notion has resulted in at least one very strange sign, shown here:
Sanderson, May 2017
That was taken looking west on I-270 at its interchange with I-25. Straight ahead on the Boulder Turnpike is the east "beginning" of US 36... that is, assuming one disregards the 1300-mile segment of US 36 behind the camera. (Incidentally, heading the opposite direction, there is a "Begin I-270" assembly, but it is not accompanied with an "End US 36" sign.)