Approximate location — plotted from published sources, not a site visit, and not a guarantee of access.
A polished marble boundary monument near the Pacific marks the western starting point of the 1849–1851 land survey that fixed the U.S.–Mexico line after the Treaty of Guadalupe Hidalgo. From the United States, the marker is reached via Border Field State Park’s Monument Mesa picnic area; the current border fence stands a short distance north of the stone, so it is viewed through the barrier. Interpretive signs on the mesa recount the survey and Friendship Park dedications.