More about the Chamizal from the National Park Service:

"In 1968, Congress established Chamizal National Memorial to commemorate the Chamizal Convention (treaty) of 1963. The Chamizal treaty finally ended a long-standing border dispute between the U.S. and Mexico

...The memorial fosters goodwill and understanding between the people of the United States and Mexico and provides a center to present activities that celebrate cultural exchange."

Will have to go back sometime when it's not dark.