{"nrhp_refnum":"81000156","name":"Colorado Street Bridge","other_names":[],"category":"structure","location":{"address":"Colorado Blvd.","address_restricted":false,"city":"Pasadena","county":"Los Angeles County","state":"CA","lat":34.14464503100004,"lon":-118.16462822099999,"geom_source":"nps_gis"},"listed_date":"1981-02-12","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Commerce","Engineering","Transportation","Architecture"],"significance_levels":["state"],"summary":{"what_it_is":"A reinforced concrete open spandrel arch bridge carrying Colorado Boulevard over the Arroyo Seco in Pasadena, Los Angeles County, California, built 1912-13 to designs by the engineering firm Waddell and Herrington.","why_significant":"The nomination presents it as a technically and visually impressive engineering work, proclaimed the highest concrete bridge in the world when it opened in December 1913. It is described as a transitional design combining modern scale with period finish and detail. It also contributed to Pasadena's growth by linking the city to Los Angeles and became an object of civic pride.","narrative":"Colorado Street Bridge carries Colorado Boulevard across the Arroyo Seco in Pasadena. Built between July 1912 and December 1913, it is a reinforced concrete open spandrel arch structure with nine large parabolic arches, a total length of 1,467.5 feet and a maximum height of about 148 feet. Waddell and Herrington designed it, but the contractor altered the alignment, curving it to reach firmer foundations at lower cost. Pasadena voters approved a bond issue, and the Los Angeles City Council contributed funds because the west end reached its territory. At completion it was billed as the highest concrete bridge in the world. Residents later campaigned to save it from demolition in 1931 and to study its preservation after a 1977 state report found severe deterioration. It remains in use, though aging, and has been named a city cultural heritage landmark and a civil engineering landmark.","period_of_significance":"1912-13","architect_builder":"Waddell and Herrington, engineers (contractor John Drake Mercereau named in the text)","architectural_style":null,"criteria":[],"status_note":"Currently in use as a two-lane bridge, with deterioration (spalling, failed expansion joints and bearings, some rusting of steel) identified in 1976-78 state studies; the balusters of the railing have been lost.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:32.098101-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/81000156.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/81000156/f5c8d08b43-800.webp","url_1600":"https://nationalhistoricalregister.com/media/81000156/f5c8d08b43-1600.webp","licence":"CC BY 3.0","author":"Bobak Ha'Eri","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:2010-1101-06-ColoradoStBridge.jpg\" rel=\"noopener\">Bobak Ha'Eri</a>, <a href=\"https://creativecommons.org/licenses/by/3.0\" rel=\"license noopener\">CC BY 3.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:2010-1101-06-ColoradoStBridge.jpg"},"district":{"nrhp_refnum":"08000579","name":"Pasadena Arroyo Parks and Recreation District","url":"https://nationalhistoricalregister.com/districts/california/pasadena-arroyo-parks-and-recreation-district-08000579/"},"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123859043","wikipedia":"https://en.wikipedia.org/wiki/Colorado_Street_Bridge_(Pasadena,_California)","wikidata":"https://www.wikidata.org/wiki/Q5148962"},"indexable":true,"url":"https://nationalhistoricalregister.com/california/los-angeles-county/colorado-street-bridge-81000156/"}