November 20, 1990
The final 14.5-mile (23.3-kilometer) section of Interstate 15 was opened to traffic near the city of Tremonton, Utah. The opening of this link of I-15 created a continuous interstate highway of about 1,430 miles (2,301.4 kilometers) between the community of Sweetgrass, Montana, at the U.S. boundary with Canada and San Diego, California (near the Mexican border).
At the dedication ceremony for the last stretch of I-15 to be completed, the Federal Highway Administration’s Regional Administrator Louis MacDonald read a message from U.S. Transportation Secretary Samuel K. Skinner. The message noted that — with the opening of the final segments of not only I-15 but also I-10, I-35, and I-40 that year — 1990 was “the greatest year for major highway completions in the history of the Interstate System.” Eugene Findlay, Director of the Utah Department of Transportation, put it even more succinctly. “We’ve done it!” he announced at the ceremony. I-15 is the 10th longest route in the Interstate System and the fourth longest north-south highway in the network.
For more information on Interstate 15, please check out https://en.wikipedia.org/wiki/Interstate_15.