{"nrhp_refnum":"97001272","name":"Mazon Creek Fossil Beds","other_names":["Mazon River","Benson Farm","Fossil Bed Farm"],"category":"site","location":{"address":"Benson Rd., 3 mi. SE of Morris","address_restricted":false,"city":"Morris","county":"Grundy County","state":"IL","lat":41.32817483350007,"lon":-88.3643399135577,"geom_source":"nps_gis"},"listed_date":"1997-09-25","is_nhl":true,"nhl_designated_date":"1997-09-25","areas_of_significance":["Science"],"significance_levels":["national"],"summary":{"what_it_is":"A fossil-collecting site of several hundred feet of exposed shale along the Mazon River (Mazon Creek) on the old Benson farm, about 3 miles southeast of Morris, Grundy County, Illinois. Fossil-bearing ironstone nodules weather out of Pennsylvanian-age Francis Creek Shale.","why_significant":"The site is one of the world's best-known sources of exceptionally preserved Pennsylvanian-age land plants and fragile animals such as insects, spiders and amphibians. It supplied what were then the oldest known land plants and animals and helped establish paleobotany in the United States through Leo Lesquereux. It is also unusual because amateur collectors found and gathered most of its fossils.","narrative":"Along the banks and bed of the Mazon River, a few miles southeast of Morris, Illinois, ironstone nodules weather out of Pennsylvanian-age shale. Many contain fossils of ferns, insects, spiders, crustaceans and early amphibians preserved in fine detail. Such fragile organisms rarely survive in the fossil record, and the nomination describes Mazon Creek as probably one of the five best-known sites of this kind in the world. Photographer Joseph Even is credited with first exploring the Benson farm locality in 1857. His specimens reached scientists including Amos Worthen, Fielding Meek and Leo Lesquereux, whose work on the fossil plants helped establish paleobotany in the United States. Most fossils here have been gathered by amateurs, who loaned or gave specimens to professionals, and Mazon Creek material is now held in museums worldwide. The setting is described as virtually unchanged, with many nodules remaining. The period of significance runs from 1857, the year of Even's discovery, to 1947.","period_of_significance":"1857-1947","architect_builder":null,"architectural_style":null,"criteria":["A","B","C","D"],"status_note":"Setting described as virtually unchanged, with many fossil-bearing nodules remaining; still attracts amateur collectors and professional paleontologists. Accessible on foot from Benson Road.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:36.003485-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/98/8915/28891598/content/electronic-records/rg-079/NPS_IL/97001272_NHL.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/97001272/6609987aa3-800.webp","url_1600":"https://nationalhistoricalregister.com/media/97001272/6609987aa3-1600.webp","licence":"CC BY 2.0","author":"James St. John","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Bandringa_rayi_fossil_shark,_Mazon_Creek_Lagerstatte.jpg\" rel=\"noopener\">James St. John</a>, <a href=\"https://creativecommons.org/licenses/by/2.0\" rel=\"license noopener\">CC BY 2.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Bandringa_rayi_fossil_shark,_Mazon_Creek_Lagerstatte.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/28891598","wikipedia":"https://en.wikipedia.org/wiki/Mazon_Creek_fossil_beds","wikidata":"https://www.wikidata.org/wiki/Q2564342"},"indexable":true,"url":"https://nationalhistoricalregister.com/illinois/grundy-county/mazon-creek-fossil-beds-97001272/"}