1 vote

Castle Rock Upper Bridge


Oblique view from northwest

In this photo, water flows from right to left

Photo taken by Roger Deschner in May 2015

License: Creative Commons Attribution-Share-Alike (CC BY-SA)


BH Photo #325488


One of two bridges on a former alignment of Boulder Canyon Highway (CO 119). When the highway was routed on a new alignment in 1953, this section of the old road, with its two bridges, was left in place, with picnic tables installed. The area around this bridge is popular today for rock climbing on Castle Rock.

NBI lists construction date as 1930, noting that dates ending in 0 are often estimates.

The two bridges are very different. This one is a steel girder/floorbeam system bridge with a jack-arch deck.


Steel girder/floorbeam bridge over Middle Boulder Creek on Old Boulder Canyon Drive (Co Rd 54A, former CO 119)
Boulder County, Colorado
Open to traffic; posted for load
Built ca. 1930; bypassed 1953, but left in place to serve recreational area
Girder/floorbeam system with jack-arch deck
Length of largest span: 28.5 ft.
Total length: 33.1 ft.
Deck width: 15.4 ft.
Eligible for the National Register of Historic Places
Approximate latitude, longitude
+39.97921, -105.45444   (decimal degrees)
39°58'45" N, 105°27'16" W   (degrees°minutes'seconds")
Approximate UTM coordinates
13/461197/4425548 (zone/easting/northing)
Quadrangle map:
Average daily traffic (as of 2016)
Inventory number
BH 67775 (Bridgehunter.com ID)
Inspection report (as of January 2018)
Overall condition: Poor
Superstructure condition rating: Fair (5 out of 9)
Substructure condition rating: Serious (3 out of 9)
Deck condition rating: Fair (5 out of 9)
Sufficiency rating: 28 (out of 100)
View more at BridgeReports.com

Update Log 

  • October 23, 2015: Updated by Roger Deschner: Added category "Jack Arch Deck"; added photos
  • May 25, 2015: Added by Roger Deschner

Related Bridges 


  • Roger Deschner - rogerdeschner [at] gmail [dot] com


Castle Rock Upper Bridge
Posted October 26, 2015, by Nathan Holth (webmaster [at] historicbridges [dot] org)

Nice work solving the mystery... as for categorization, I guess its a matter of opinion... its mostly a deck girder, but could be called a through, if barely. Even though its technically not a "plate" girder, that's probably OK to list it as that. I ran into a similar problem on my own website with a similar bridge in Canada... and I was too lazy to create a separate category :)

Castle Rock Upper Bridge
Posted October 23, 2015, by Roger Deschner (rogerdeschner [at] gmail [dot] com)

Nathan, you're right, and I was able to revisit the bridge and look underneath to confirm and get a picture. (photos above) The creek was running high, so the only way to get a picture underneath was to dangle my phone on a "selfie stick". (Useful when you have neither fishing waders nor a drone.) The photo revealed an unusual jack-arch deck.

Unfortunately, there is no category here for girder/floorbeam system bridges. Should this really be some kind of a pony girder bridge, since the support beams are higher than the deck? No category for that either, since the support girders are not composed of plates. I'll leave these questions of taxonomy to others; I took the pictures.

Boulder Canyon Drive Old Upper Bridge
Posted May 25, 2015, by Nathan Holth (webmaster [at] historicbridges [dot] org)

I think this is actually a girder/floorbeam system type bridge. Note how the outer beams rise above the roadway level, and further note the rivets in the side of the girder, which one would assume, are where the transverse floor beams are riveted.