The Border Field State Park is a very interesting state park in San Ysidro, California. It contains the US-Mexico border, the southwesternmost point of the contiguous US, and the southernmost point in the state. It is also situated within the Tijuana River National Estuarine Research Reserve, which is an important wildlife habitat and provides refuge to endangered birds.

There are quite a number of things to see at the Border Field State Park. For one, there is a fence, known as the Tortilla Wall, inside the park that demarcates the borders of the US and Mexico. On the other side of the fence is the suburb of Playas de Tijuana.

Visitors of the Border Field State Park can enjoy horseback riding, biking, windsurfing, fishing, picnicking, wildlife viewing, and hiking at the site.