Big Bend National Park

The town of Boquillas, Mexico is just across the river from the park and is 100+ miles from anywhere in Mexico, over practically non-existant roads. They do all their shopping in the US and their economy is based on giving rides across the river and selling craft items, etc. to the tourists. Needless to say they have closer ties to the US than to Mexico.
The dark area is the park.
The arrow points to Boquillas.