{"nrhp_refnum":"00000398","name":"Allegheny River Lock and Dam No. 4","other_names":[],"category":"structure","location":{"address":"1 River Ave.","address_restricted":false,"city":"Natrona","county":"Allegheny County","state":"PA","lat":40.613337299500046,"lon":-79.71601503385085,"geom_source":"nps_gis"},"listed_date":"2000-04-21","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Transportation","Maritime History","Economics","Engineering"],"significance_levels":["state"],"summary":{"what_it_is":"A U.S. Army Corps of Engineers navigation lock and dam on the Allegheny River at Natrona, Allegheny County, Pennsylvania, with a lock, dam, esplanade, operations building and locktender's house. It was constructed in 1920-1927 by the Corps, which hired the labor itself rather than using a contractor.","why_significant":"The nomination argues the lock and dam is significant under Criterion A as part of the Allegheny River slackwater navigation system, which allowed barge access and industrial growth along the lower river from Natrona to Freeport. It is also argued to be significant under Criterion C as a representative example of lock and dam construction of 1920-1927, retaining its original appearance and function with a high degree of integrity.","narrative":"Lock and Dam No. 4 sits on the Allegheny River in Natrona, Allegheny County, about 24.2 miles upstream from the river's mouth. The U.S. Army Corps of Engineers built it in 1920-1927 with its own hired labor after contract bids came in far above estimates. The facility created slackwater navigation for commercial barges and towboats along a stretch of roughly 72 miles of the river and gave steel mills at Natrona and a rail distribution center at Freeport water access. The lock measures 56 by 360 feet with a lift of 10.6 feet. Its two-story Moderne concrete operations building has a rounded upstream end. After the St. Patrick's Day flood of 1936 weakened the dam's south abutment, reconstruction in 1937-1938 added steel sheet piling and roughly 2.5 acres of derrick stone. The lock is regarded as a representative example of 1920s lock and dam construction.","period_of_significance":"1920-1927","architect_builder":"U.S. Army Corps of Engineers (not contracted)","architectural_style":"Moderne","criteria":["A","C"],"status_note":"Operating lock; the locktender's house is presently vacant and the powerhouse has been altered, with gates and valves converted to electric operation in 1994-1995.","vacant_flag":null,"machine_generated":true,"model":"claude-haiku-5-5","prompt_version":"v1.1-2026-10-29","generated_at":"2026-10-29 17:11:37.928965-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_PA/00000398.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/00000398/5a029f9433-800.webp","url_1600":"https://nationalhistoricalregister.com/media/00000398/5a029f9433-1600.webp","licence":"Public domain","author":"U.S. Army Corps of Engineers","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Allegheny_River_Lock_and_Dam_No.4.jpg\" rel=\"noopener\">U.S. Army Corps of Engineers</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Allegheny_River_Lock_and_Dam_No.4.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/71992252","wikipedia":"https://en.wikipedia.org/wiki/Allegheny_River_Lock_and_Dam_No._4","wikidata":"https://www.wikidata.org/wiki/Q4731336"},"indexable":true,"url":"https://nationalhistoricalregister.com/pennsylvania/allegheny-county/allegheny-river-lock-and-dam-no-4-00000398/"}