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Isthmus Slough Bridge


Isthmus Slough Bridge

Photo taken by Historic American Engineering Record

View photos at Library of Congress

BH Photo #138151


Through truss bridge over Isthmus Slough on FAS A-396
Coos County, Oregon
Replaced by a Concrete Box Girder Bridge in 2004
Built 1955, Replaced 2004
- P. Mervyn Stephenson (Bridge Engineer)
The Isthmus Slough Bridge is significant as a good example of the bascule bridge type. This bridge is unique within the Oregon context at it is the only known bascule structure that utilizes a block and tackle lifting mechanism, as opposed to the more common motorized lifting mechanism. The lack of motorized technology distinguishes this structure within Oregon's context of moveable bridges. The Isthmus Slough Bridge is also significant as a late example of the bascule type within Oregon, as it is only one of three bascule spans built after WWII.
(HAER OR-144 - Isthmus Slough Bridge)
Length of largest span: 85.0 ft.
Total length: 686.1 ft.
Deck width: 24.0 ft.
Vertical clearance above deck: 14.1 ft.
Eligible for the National Register of Historic Places
Approximate latitude, longitude
+43.30083, -124.20861   (decimal degrees)
43°18'03" N, 124°12'31" W   (degrees°minutes'seconds")
Approximate UTM coordinates
10/401969/4794931 (zone/easting/northing)
Quadrangle map:
Coos Bay
Inventory numbers
OR 02300A (Oregon Dept. of Transportation structure number)
BH 29928 (Bridgehunter.com ID)

Update Log 

  • April 20, 2009: Posted HAER photos
  • December 4, 2008: Updated by Michael Goff: Updated Status


  • Mike Goff - michael [dot] goff [at] hotmail [dot] com
  • HAER OR-144 - Isthmus Slough Bridge
  • Douglas Butler