{"nrhp_refnum":"11000130","name":"Mills Building","other_names":["Anson Mills Building"],"category":"building","location":{"address":"303 N Oregon St","address_restricted":false,"city":"El Paso","county":"El Paso County","state":"TX","lat":31.76093210600004,"lon":-106.48940539299997,"geom_source":"nps_gis"},"listed_date":"2011-03-21","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Architecture","Community Planning and Development","Engineering"],"significance_levels":["local"],"summary":{"what_it_is":"A twelve-story reinforced concrete commercial office building at 303 North Oregon Street in downtown El Paso, Texas, designed by Henry C. Trost of Trost & Trost. It was built in two phases, eight stories in 1911 and twelve by 1915.","why_significant":"The nomination argues it is significant under Criterion C as the work of Trost & Trost and as an early tall building of monolithic reinforced concrete, the tallest and largest of its kind in the United States when completed. It is also significant under Criterion B for its association with Anson Mills, who surveyed and platted El Paso and called the building his greatest monument.","narrative":"Rising twelve stories at the corner of Oregon Street and Mills Avenue, this concrete office building anchors downtown El Paso opposite San Jacinto Plaza. Henry C. Trost of Trost & Trost designed it for Anson Mills, who had surveyed and platted the city. Eight floors were finished in 1911, and four more were added by 1915. Built of monolithic concrete poured in place, it was then the tallest and largest building of its type in the United States. Its rounded corner, repeating windows and clear base, shaft and cornice echo Chicago School tall buildings, though the concrete construction forced simpler ornament. Alterations in 1974 replaced the windows with mirrored glass and stripped much of the interior. A certified rehabilitation completed in 2010 restored the historic window pattern, rebuilt the entry porticoes, revived one marble-stair lobby and added a brick wing of 20,000 square feet. The building is recognized for its architecture, engineering and its link to Mills.","period_of_significance":"1911-1915","architect_builder":"Henry C. Trost, Trost & Trost","architectural_style":"Late 19th and Early 20th Century Movements: Commercial style","criteria":["B","C"],"status_note":"A certified rehabilitation was completed in 2010, removing 1974 mirrored-glass bands, restoring the historic window pattern and one lobby, and adding a wing; current use is commercial/business.","vacant_flag":false,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:54:23.980545-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/opastorage/live/98/9688/40968898/content/electronic-records/rg-079/NPS_TX/11000130.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/11000130/93056ea16a-800.webp","url_1600":"https://nationalhistoricalregister.com/media/11000130/93056ea16a-1600.webp","licence":"CC BY-SA 3.0","author":"Camerafiend at English Wikipedia","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Anson_Mills_Building.jpg\" rel=\"noopener\">Camerafiend at English Wikipedia</a>, <a href=\"http://creativecommons.org/licenses/by-sa/3.0/\" rel=\"license noopener\">CC BY-SA 3.0</a>, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Anson_Mills_Building.jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/40968898","wikipedia":"https://en.wikipedia.org/wiki/Anson_Mills_Building","wikidata":"https://www.wikidata.org/wiki/Q4770731"},"indexable":true,"url":"https://nationalhistoricalregister.com/texas/el-paso-county/mills-building-11000130/"}