The “zero” milestone of the Old Spanish Trail is a hard-to-miss, spherical monument made of coquina shells nestled in the underbrush.

The milestone marks the end of the Old Spanish Trail auto highway that once linked San Diego, California and St. Augustine, Florida.

The Old Spanish Trail (OST) was an early 20th century auto highway project intended to provide a continuous highway route from California to Florida, linking together the southwestern and southern states.

Planning and construction of the OST highway system began in 1915 and the highway was officially opened for travel in  1929. The highway’s name, the Old Spanish Trail, also pays homage to the Spanish heritage and missions of the southwest and the south.

The Old Spanish Trail highway follows what eventually became known as U.S. Highway 80 in the southwest and U.S. Highway 90 in the south.