{"nrhp_refnum":"74000550","name":"Initial Point of Boundary Between U.S. and Mexico","other_names":["Western Land Boundary Marker No. 258, U.S. &amp","Mexico"],"category":"site","location":{"address":"S of Imperial Beach off Monument Rd.","address_restricted":false,"city":"San Diego","county":"San Diego County","state":"CA","lat":32.53455201200006,"lon":-117.12290020799998,"geom_source":"nps_gis"},"listed_date":"1974-09-06","is_nhl":false,"nhl_designated_date":null,"areas_of_significance":["Politics/Government"],"significance_levels":["local"],"summary":{"what_it_is":"A site on the international boundary near Border State Park in San Diego, California, marking the initial point of the U.S.-Mexico boundary, first established in 1849 as a cairn and later marked by a marble obelisk erected in 1851 and reconstructed in 1894.","why_significant":"Monument No. 258 marks the initial point of the boundary fixed by the Joint Commission under the Treaty of Guadalupe Hidalgo. It is the westernmost boundary marker between the United States and Mexico and marks the southwestern corner of the continental United States.","narrative":"Monument No. 258 is a marble obelisk at the Pacific end of the border between the United States and Mexico, reached through Border State Park southwest of San Diego. It began in 1849 as a cairn of rocks, set after the Treaty of Guadalupe Hidalgo. A white marble shaft made in New York was carried around the Horn on the USS Supply and dedicated at the site in June 1851. Visitors had so damaged it by 1894 that the Barlow-Blanco Commission had it renovated, rebuilt on the spot and fenced. The inscription on its west face names the initial point of the boundary, established by the Joint Commission on 10 October 1849, with John B. Weller as U.S. Commissioner and Andrew B. Gray as U.S. Surveyor. As the westernmost boundary marker, it fixes the southwestern corner of the continental United States. The monument straddles the line, half in each country, and is under the jurisdiction of the International Boundary and Water Commission.","period_of_significance":"19th Century","architect_builder":null,"architectural_style":null,"criteria":[],"status_note":"Condition is stated as good and altered, at its original site; the 1894 reconstructed marble monument still stands, with normal wear and some slight vandalism. The south half of the monument is in Mexico and the north half in the United States.","vacant_flag":null,"machine_generated":true,"model":"claude-sonnet-5-5","prompt_version":"v1.0-2026-10-29","generated_at":"2026-10-29 02:55:31.966021-05","source_pdf":"https://s3.amazonaws.com/NARAprodstorage/lz/electronic-records/rg-079/NPS_CA/74000550.pdf"},"photo":{"url_800":"https://nationalhistoricalregister.com/media/74000550/ac501176b0-800.webp","url_1600":"https://nationalhistoricalregister.com/media/74000550/ac501176b0-1600.webp","licence":"Public domain","author":"national park service","credit_html":"<a href=\"https://commons.wikimedia.org/wiki/File:Monument_marking_the_Initial_Point_of_Boundary_Between_U.S._and_Mexico_(1974_photo).jpg\" rel=\"noopener\">national park service</a>, Public domain, via Wikimedia Commons","source_page":"https://commons.wikimedia.org/wiki/File:Monument_marking_the_Initial_Point_of_Boundary_Between_U.S._and_Mexico_(1974_photo).jpg"},"district":null,"sources":{"nps_snapshot_date":"2026-05-22","nara_catalog":"https://catalog.archives.gov/id/123860892","wikipedia":"https://en.wikipedia.org/wiki/Initial_Point_of_Boundary_Between_U.S._and_Mexico","wikidata":"https://www.wikidata.org/wiki/Q2892431"},"indexable":true,"url":"https://nationalhistoricalregister.com/california/san-diego-county/initial-point-of-boundary-between-u-s-and-mexico-74000550/"}