The Old Spanish Trail is not really Spanish, nor is it particularly old, at least for St. Augustine. The "trail" began in 1915 as a transcontinental highway for automobiles, connecting St. Augustine in the east to San Diego in the west. The Old Spanish Trail Association began in Mobile, Alabama, where they saw the commercial benefit of having an east/west highway connecting the new north/south Jackson and Dixie highways. Thus, the Old Spanish Trail began in a city known for its French heritage.
These new highways brought automotive tourists and their money to the communities along the roadways. During World War I, advocates of the Old Spanish Trail (and other national highways) promoted its importance as a military road, vital for national security and defense, anticipating Eisenhower's Interstate Highway system by several decades. In the 1920s, Harral B. Ayres, the Old Spainish Trail Association's director, encouraged the notion that the highway followed old Spanish roads, using the romance of the past to promote tourism.
The terrain the highway was to cover in the southeastern United States hampered construction - bridges were needed over the many rivers and swamps of the coastal South. The Old Spanish Trail was not completed until 1929, an event marked by a three-day celebration in St. Augustine, and the dedication of this commemorative marker (which since has been moved twice).
Each year, on the last weekend of April and the first weekend of May, Crestview, Florida, holds the Old Spanish Trail Festival. This year will be the event's 53rd anniversary, and is only 11 days from now!
The Story of the Old Spanish Trail, by Harral B. Ayres (Old Spanish Trail Centennial)